No they're right, they literally just run and jump underwater

Yet despite all these adaptations for life in the water, hippos can't swim—they can't even float! Their bodies are far too dense to float, so they move around by pushing off from the bottom of the river or simply walking along the riverbed in a slow-motion gallop, lightly touching the bottom with their toes, which are slightly webbed, like aquatic ballet dancers.

https://animals.sandiegozoo.org/animals/hippo

Honestly that's scarier to me

Man, i actually have in a little riverboat in kenya. It's absolutely terrifying. There were some other tourists on the boat who treated it like a circus show the hippo did for them. They cheered every time it jumped out of the water getting closer and closer. I was sitting very close to the boat captain, who was sweating bullets.