No, they're pointing out the obvious. Newsweek isn't what it used to be, and the claims are all sourced from Ukraine, with no external on the record confirmations, yet.
Ukrainian media has a moral obligation to service the propaganda needs of the war. That's neither good, nor bad, that's just a part of being in an existential war for survival. I don't blame them for it, and I'm certainly not bashing them for, I'm just pointing out reality.
I can't speak for the person you're responding to, but I have no trouble understanding why North Korea would send thousands of support personnel to Ukraine as the logistical tail to support their weapons platforms. Western nations have been doing the same thing inside Ukraine.
Maybe the story is true, it's possible. But I'm going to need to see better sources provided then a Kyiv Post article citing unnamed Western officials or Newsweek using Ukrainian articles as their source information.
That's it. If anything, it's more unreasonable to not be skeptical of early reports coming from any war zone, whether you want to believe them, or not.