Yes, North Korea really did threaten a second and third "strong physical retaliatory blow"

As first noted in the LAT article, the KCNA did indeed report that the Korean People's Army has threatened further attacks. The same article blames (again) South Korea for firing into "the territorial waters of the DPRK" (actually waters south of the NLL controlled by South Korea since the Korean War) and blames the US for not keeping its dog on a leash (a criticism I've made of China).

For your edification (with italicized editorial content added):

Panmunjom Mission of KPA Sends Notice to U.S. Forces Side

Pyongyang, November 25 (KCNA) -- As already reported, the south Korean puppet war-like forces Tuesday committed another grave military provocation such as firing shells into the territorial waters of the DPRK side in the West Sea of Korea.

The revolutionary armed forces of the DPRK took a prompt and resolute physical counter-action against the provocateurs who dared fire even shells into the territorial waters of the DPRK side while staging the maneuvers for a war of aggression against it codenamed Hoguk.

This once again confirmed the unshakable stand of the army of the DPRK not to allow even in the least anyone to encroach upon its inviolable territorial waters.

There came from the U.S. forces side a notice blaming the DPRK under the absurd charge that the recent shelling took place in the area under its military control and it was a "violation of the Armistice Agreement." [Kushibo's note: I'm surprised they even acknowledge the US position as strongly as they do.]

The Panmunjom Mission of the Korean People's Army today sent the following notice to the U.S. forces side in connection with its attempt to misrepresent the incident, while thoughtlessly shielding the south Korean puppet forces who dared make a preempt shelling at the DPRK:

The south Korean puppet warmongers' firing of shells into the territorial waters of the DPRK side in the West Sea of Korea [actually South Korea-controlled waters south of the NLL] on Nov. 23 was a premeditated and deliberate military provocation from A to Z and a war action in fact [It might be easier to just list what is not a military provocation or war action, since it seems to be anything Seoul ever does].

On Nov. 22, the south Korean puppet forces made no scruple of announcing that they would fire shells into the territorial waters of the DPRK side with artillery pieces they deployed on Yonphyong Island while staging Hoguk exercises for a war of aggression against the DPRK [note that South Korea defending its own waters is now labeled an act of war for which Pyongyang sees fit to launch actual military assaults], straining the situation on the Korean Peninsula.

In this connection the DPRK side sent a telephone notice to the south Korean puppet military at 8 a.m. on Nov. 23, strongly urging it to immediately cancel the plan for firing shells into the territorial waters of the DPRK side. In the notice the DPRK side seriously warned that if it paid no heed to this demand, it would face a resolute physical counter-strike and would be held fully responsible for all the ensuing consequences [How did we know that this time you would actually mean it? And why did it have to involve killing civilians?].

The south Korean puppet forces, obsessed by hysteria for invasion of the DPRK [I'm sure you like thinking that, but the truth is your own actions are making it more likely], committed such reckless military provocation as preempting the firing of shells into the territorial waters of the DPRK side in the West Sea of Korea by mobilizing artillery pieces deployed on Yonphyong Island, defying the repeated efforts made by the DPRK to prevent military conflicts and preserve peace and stability in the said waters.

The island, therefore, played the role of an outpost from which a military provocation was perpetrated against the DPRK and it deserved punishment meted out by the army of the DPRK according to its self-defensive measure. ["The island... deserved punishment." Why do I feel like I'm in an episode of Lost?]

The Panmunjom Mission of the KPA in the notice particularly emphasized the fact that the U.S. forces side, too, is to blame for the incident.

The West Sea of Korea turned into disputed waters always fraught with the danger of confrontation and clash between the north and the south because of the illegal "northern limit line" unilaterally fixed by the U.S. inside the territorial waters of the DPRK. The U.S., therefore, cannot evade the blame for the recent shelling. [Is there anything the US can't be blamed for?]

If the U.S. forces side truly desires the detente on the Korean Peninsula, it should not thoughtlessly shelter the south Korean puppet forces but strictly control them [Change US to China and south to North and you've got yourself change I can believe in] so that they may not commit any more adventurous military provocations such as intruding into the waters of the DPRK side and shelling for the purpose of defending the illegal "northern limit line".

The prevailing situation goes to prove that it is the south Korean puppet forces which actually violated the Armistice Agreement and it was none other than the U.S. which sparked off the conflict in the above-said waters. [War is peace. Freedom is slavery. We have always been at war with Southkorea.]

This being a hard reality, the U.S. and the south Korean puppet forces are foolishly contemplating an additional provocation aimed to orchestrate another farce and charade such as the "Cheonan" case while kicking up rows and holding confabs one after another such as the declaration of a "state of emergency" and "a meeting of ministers in charge of security," far from drawing due lesson from the recent shelling.

The Korean People's Army will deal without hesitation the second and third strong physical retaliatory blow if the south Korean puppet warmongers commit another reckless military provocation out of all reason. [The money shot.]

The U.S. would be well advised to drop its inveterate bad habit of pulling up others, falsifying the truth about the situation. 

This would be hilarious if it weren't so serious. The second to the last paragraph makes clear that they are intending further attacks. The conditional (i.e., "if South Korea doesn't commit another provocation") is an impossibility, given that they have defined South Koreans patrolling the waters south of the de facto border — i.e., maintaining the integrity of its own territory — as a "provocation."

South Korea has two choices: Hold its ground (so to speak) and risk another military confrontation, or give in to threats of military confrontation and undermine control of its own waters.