To be quite honest, when I saw this (The video of it) some months back, I thought it was cute! The man put the tank together, used a tiny little net and a little bubbler and everything for it. The fry are so tiny they didn't seem stressed at all but the space, swimming around happily. And the creator said it was temporary. It didn't seem cruel at all and didn't look like he was mistreating the fish.
I agree, there are some things that shouldn't be done "For art" but this one doesn't strike me as cruel at all.