I think that all sentient beings have personhood, and that personhood isn't limited to homo sapiens. Dogs have feelings and personalities, and they can feel ill and get hurt. And they grieve. Dogs are definitely people. You just think they don't have personhood bc they can't talk. But language is the only thing missing.
Plus, we are actually animals too.
The dogs look really happy at the dog swim and look as if they're enjoying themselves, just like human people do.