look, Its exactly as fireheart saysTThat isn't how people consciously make decisions normally. That's really fucking weird actually. The altruistic impulse is because people get distressed when they see other people suffer, not because they need to work out their family issues through a proxy.
I wrote just that... (and I didn't edit that part)
he saved her and then realized "hey, she looks like my kawaii imouto <3" and helped her even more
and about the "men help women more than they would help other men" part
its a basic instinct, its just that way... I don't really want to get into it and I can't promise 100% acuraccy but the core should be right:
Women are flight animals, Men are not... evolution "made" (as in darwin's theory... and not lamarck-style) women weak, because they have to feed their offspring, muscles would drain too much energy... they want to be protected
Men are stronger, normally they got the will to fight, they got muscles and power... they want to protect the women, which is weaker. both the "will to be protected" and the "will to protect" play a significant role in how you would react in a situation where you have to help either a man or a woman.
the so called "gentleman reflex" is very similiar to this (I don't know if that is the correct english translation)
and its a given that family members or people who resemble such members are being prioritized