You quote part of a sentence about dolphins from the beginning of the transcript.
1. The context is Cowen posing a quirky, ice-breaker kind of question that entertain some counter-factual assumptions to get a conversation rolling. Not unusual in these kinds of pod conversations. The quirky setup and the laugh is evidence that strict realism about real world dolphins is not assumed by Singer and Cowen there. For example Cowen says "We explain to the dolphin that you’re Peter Singer, right?", but from Singer's other work it is clear that he doesn't think science into any dolphin so far has found cognitive capacity necessary to understand the concept of a well known academic moral philosopher who has written the kind of arguments Peter Singer is well known for. The best interpretation is that what is happening at the start of the conversation is merely a loose way to imagine and talk about an outside view on the harm humans do to other animals.
2. Setting 1 aside you ascribed a view about not just Dolphins but "anything non human" to Singer. What's your basis for that?
3. As for the "moral superiority" ascription, Singer imagining a dolphin asking him "Why have you failed to stop humans treating animals so badly?" doesn't imply that Singer thinks dolphins (in general, or that imagined kind) have "moral superiority". For one, real humans have already asked that question so the imaginary dolphin is at most on par, not superior, in asking it. Secondly a moral thinker (real human or imaginary dolphin) may be able to point out some moral problems or ask moral questions while at the same time be unable to refrain from harmful behaviour and unable to understand other moral problems, including those where they're themselves part of the problem. So nothing Singer says there implies that he thinks dolphins (real or imagined) are morally superior in the sense of never causing any harm or understanding all moral problems better than humans or anything like that.