Funny? YesCute? Yes. But seriously, why punish a fish for something you the fish-keeper have done? Moreover, as stated above, fish don't know right from wrong. They are instinct-driven biological machines. The keeper is responsible for everything "bad" that happens in their "artificially created mini underwater world".
It is not punishing them, just reconditioning them. Removing an aggressive fish and allowing the remaining fish to establish a new pecking order before returning the aggressive fish can sometimes avoid having to rehome said aggressive fish. Ideally you would place it in a spare tank or quarantine. If one is not available, I guess you can get creative. The bag is just a comical extreme and I assume the fish in the picture was posed for the purpose of comedic relief and returned to its tank. I think the comedy lies in that many of us care for our fish like they are our children and assign them human characteristics and feelings. Hence, if your child misbehaves and you give him/her a time-out...well, why not for our fish. But of course we know the picture is a joke and that a fish is a fish is a fish...OR IS IT?