FYI, apparently, the crayfish isn't a pet. this is the equivalent of feeding mice to a pet snake, or crickets to a pet lizard. I was confused as to why the aquarium owner didn't intervene, then I looked it up.
Also, the youtube comments for this video are surprisingly good.
I had a pet crayfish. I found it in a creek, and put it in the fish aquarium. I didn't have any fish badass like that pufferfish, so a few got eaten by the crayfish.