That comment is demeaning, unhelpful, and in very bad taste. It's the comment that the delete functionality on GitHub was made for. However, one of the other participants in the thread immediately called out this comment. So you have a constructive dialog, a single bad actor, and said single actor being called out by the people having the constructive dialog. That doesn't sound like an unhealthy community to me, to be perfectly frank.
I agree that the comment is in bad taste but what I don't see this being considered a "far, far, far over the line." comment when I take into consideration that it had been posted in reply to the maintainer's also dismissive comment "this patch is boring" so, yes, the user has definitely been rude, but chances are it's a visceral response too.
Otherwise if that event is far far over the line I wonder what out of the blue insults or death threats qualify as.
