I can only speculate as I didn't write that post, but by my reading they were just stating their belief that AI is likely to lead to human extinction, not that they were happy about that outcome.

Personally, I think there's a worryingly high chance that ourselves or our kids will live in a dead, desertified, apocalyptic hellscape of a planet after we hit 5+ degrees of warming, but saying that doesn't mean I _want_ it to happen. In fact, I would prefer it not to!