It's definitely on his part for lagging. Maybe it can't be helped but it's his responsibility. Should you call him out for it? Yes. Does he deserve to be called out? Also yes.

Flaming is never good though. This adds to toxicity, it's just extreme raging. Flaming is inexcusable because it can just be replaced with hard facts and a logical explanation. There's no reason to pull out people's parents or age or vulgarities just because of this game we all collectively love to hate. Unbanning flaming gives people free reign to throw out whatever german or spanish vulgarities they learned that day and chuck it into a game without consequences. I don't think flaming should be allowed but I'm sure there are better fitting punishments for it.