Why the hell are people always so eager to dismiss other people's goodness?
Pretty much everybody agrees that sometimes people can be horrifically cruel. Nobody reads a story about a serial rapist killer of children and thinks "well, but was he really a bad person? Let's look at this from a biological standpoint, killing children means less competition for any future children he might possibly have on day in the future!" No, pretty much everybody looks at the story and thinks, man, what an evil asshole!
But when people are awesomely heroic, it's like a rush to try and prove that they weren't really heroic, that deep down they must have been motivated by selfish reasons. He died to save his girlfriend, so clearly he was thinking of protecting his own genetic material because sooner or later he probably would have knocket her up! Clearly he must have thought that he could save them both so saving his gf would let him be happier later. Clearly he was just doing that to make himself feel good.
Nevermind the fact that nature is all about conserving energy. A predator will stop chasing its prey if the pray manages to get a small head start. A mother will eat her cubs if there aren't good enough chances for the survival of the offsping so she can take most of the nutrients back. In nature, it simply makes no biological sense whatsoever to risk your life for a mate that might possibly maybe one day give you offspriong, especially when potential mates are all over the place (it's not like there is a shortage of women, we are 51% of the world population). And the fight-or-flee response in the face of a friggin' hurricane makes it highly unlikely that the guy just assumed he could save them both. And feeling good may happen after you do a good deed, not while you are getting crushed under tons of freezing water, especially since the whole thing happened all of a sudden so he had no time to think about possible long-term benefits.
Seriously, why are people bending over bakwards to try and find any justification for what happened except "he was a genuinely kind and selfless person"? There is being a cynic, and then there is being a misanthrope.