I would think they are talking about non-vegans but trying to be a bit coy.

It’s treating animals in a way that you wouldn’t treat humans because it’s wrong/illegal.

Keeping them as pets, breeding them, caging them (slavery)

Eating them, or using their products (cannibalism)

Wearing their skins (is there even a name for that?)

I came across it when I was young as a family member worked in animal activism and was horrified that I had a pet.