Altruism, yes. It would be nonsensical for anyone to claim that they would essentially risk their own life for their pet and somehow gain some genetic benefit from that...
Well, there are some people who probably would, and in some cases people may do that. I'm not one of them (Skipper can get herself out of the burning house, she smart enough to figure out the way) and I would only go so far as to leave the door open as i run... but some people may go back for beloved family pets. Emotion makes humans dumb.