Nah, this is often not considered swimming in major publications and by zoos.

National Geographic

https://www.nationalgeographic.com/animals/mammals/facts/hip...

> Hippos cannot swim or breathe underwater, and unlike most mammals they are so dense that they cannot float. Instead, they walk or run along the bottom of the riverbed. Because their eyes and nostrils are located on the top of their heads, they can still see and breathe while underwater. When totally submerged, the ears and nostrils shut tight to keep the water out, and hippos can hold their breath for five minutes.

San Diego Zoo

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

> 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.

Also echoed by Cincinnati Zoo and I'm certain many other experts.

But yes, it is maybe pedantic to define swimming!

However, even if you'd be kind to this LLM and say "Alright, sure, it's kinda swimming", it's still wrong in terms of being among particularly good mammal swimmers! This is just flat out wrong no matter how you look at it. They're terrible at it but have evolved to not need to be awesome at this.