Dolphins don't save humans because of altruistic reasons towards our species. Their own offspring behaves similarly when drowning, and they mistake a drowning human to potentially drowning dolphin.
This is somewhat analogous to your explanation of dolphins acting altruistically toward humans because we resemble their young when struggling in the water.
In the same way, it would be very hard for most of us to ignore a lost crying puppy wandering down the street.
Humpback also have spindle (mirror) neurons in their brains, those are thought to be related to cooperation, empathy, etc. Humans have them too, but not many other species (https://www.sciencedaily.com/releases/2006/11/061127111607.h...).
It is good to not anthropomorphise, but we really should finally move away from Descartes' view on animals being simple automatons.