Yeah sorry I assumed that they didn't just spontaneously all suicide.
It's not actually as likely as you say. Remember 500 of these ships landed in Japan, without survivors. It seems like the survival rate of these ships is way lower than you'd expect. If you have 500 ships that break down due to engine failure and drift to Japan, I'd expect at least one to have a guy on it who ate the corpses of all the other guys. Humans are pretty hardy like that.
That one ship that went into the area did mention that the Chinese ship tried to ram them, so I wouldn't be surprised if they're disabling the NK ships rather than them just all randomly floating away, like 500+ times. Blown off course, engines broke down, ran out of supplies etc. Far more of them should in fact be limping into foreign ports, not all washing up as skeletons.
Chinese fishing boats are famously aggressive, often armed and known for ramming competitors or foreign patrol vessels, according to U.S. Navy officials and maritime security specialists. Chinese media often depict the country’s maritime clashes with other nearby Asian nations as an extension of ancient China's Three Kingdoms, which fought a fierce three-way battle for supremacy.
Tensions between Seoul and Beijing increased in 2016 after a Chinese vessel, illegally fishing in South Korean waters, sank a South Korean Coast Guard cutter. The cutter was in South Korean waters and was trying to stop a Chinese fishing ship that allegedly had been caught fishing illegally when it was rear-ended by another Chinese ship.
If they're willing to sink South Korean navy vessels, I think they're capable of ramming NK fishing boats.