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