I'd be bothered, too. If there were plans and they blew them off without calling, that's rude. I'd be annoyed, but I wouldn't get too upset until I heard the circumstances (was there miscommunication, was there a family emergency, etc.). But if they're 2 hours late and unreachable, I would assume they're not coming at all and go about my day.
I think we've had it all happen:
-- friends who never show
-- friends who call at the last minute because they got a better offer
-- friends whose parents arrive 2 hours late for pick up (because they were shopping and decided to stop for dinner... meanwhile, I'm trying to decide whether to feed the kids dinner or not, because it's way past dinner time but I thought his mom was going to pick him up before dinner!) That child has not been invited back... and they redistricted the school district and he ended up at another school, so he and DS have fallen out of touch.
ETA: Just read your update. Rude. Grrr. I'd be annoyed. (Is this a playdate with your son, or did you agree to do childcare today during school break?)