You could say "he's behaving irrationally" or even "he seems to be experiencing severe burnout".. But your exact phrasing is way too close to an "online diagnosis" (which is not a valid way to assess a mental illness - afaik no psychiatrist would ever diagnose anyone without ever talking to a person). On top of that, it's too close to an ad hominem - even if you didn't mean it that way.

Everyone is fighting their own demons. Some people are neurodivergent, but nothing good ever happens from an unsolicited "diagnosis" or slapping labels like "unglued". Every one of us can snap under enough pressure. Let's not go there.