Dolphins are of course very 'dumb'; its taken years of hard research to come up with any evidence of intelligence, and its all indirect. Why we even bothered? Probably because of their large-ish brain, which turns out is an elaborate visual cortex (ok, sonar cortex, same thing).
They play; they have family units, at least for a while. Is this intelligence? Crows do all that too; many other mammals also.
Caring for humans is anecdotal. My favorite one is, people adrift from shipwreck get pushed to shore by dolphins. This suffers from observer bias - dolphins love to play with floaty things, and push them around. All the sailors pushed out to sea don't tell their storey.
May dolphins be intelligent? Ok, sure. But as they don't have societies, inventions, any more language than many birds, their intelligence is very much more similar to other 'lower' animals than human.
Maybe its a different kind of intelligence? That's reaching, kind of making up things to fit a desired conclusion, but ok. Then the 3rd argument in my original post: its a kind of intelligence that doesn't extend to saving one anothers' lives. If even one escaped dolphin mentioned "I got out of there; all my family are missing, plus two other pods I know of; maybe we should stay away from that bay", we would have fabulous evidence of an intelligent society sharing the planet with us. Observably not happening, so one could conclude (I never said I conclude this, thats your projection) that they are of an intelligence too small to permit that communication. In fact, occams razor damands this conclusion.