The pattern of brain injury they're referring to is probably "anoxic brain injury." Botulism itself doesn't cause that, but it certainly can cause respiratory failure (by paralyzing the phrenic nerve), which can then cause anoxic brain injury. There's no reliable way to tell at this point whether botulism was the cause in Warmbier's case (there's no test to find out after the fact). I'm an MD.

Of course the NK story is very suspect. We need more information, but it seems unlikely that we'll get it.

We're sure that he wasn't because he was beaten though, right?

There hasn't been any US prisoners in NK who were physically abused during their stay for PR purposes. I'm curious if he sustained a fall or some other accidental injury. Maybe he caused it himself and didn't get proper treatment.

He was held for an unusually long time compared to most people.