Generally speaking, the terms man and woman are reserved specifically for humans. I couldn’t tell you why, but I suppose it doesn’t really matter.
For pets, the use of boy/girl probably does have a lot to do with how people tend to infantilize their companion animals.
Additionally, the boy / girl terminology is often generalized to cover all animals, particularly when adults are interacting with children and by extension when children are interacting with each other. It’s not uncommon to have a child ask something like “is that a boy rabbit or a girl rabbit?” but it is a little unusual to hear an adult ask another adult that same question, unless it’s sort of tongue-in-cheek or maybe in the presence of kids.
Generally speaking, the terms man and woman are reserved specifically for humans. I couldn’t tell you why, but I suppose it doesn’t really matter.
For pets, the use of boy/girl probably does have a lot to do with how people tend to infantilize their companion animals.
Additionally, the boy / girl terminology is often generalized to cover all animals, particularly when adults are interacting with children and by extension when children are interacting with each other. It’s not uncommon to have a child ask something like “is that a boy rabbit or a girl rabbit?” but it is a little unusual to hear an adult ask another adult that same question, unless it’s sort of tongue-in-cheek or maybe in the presence of kids.
I do call my doggo ‘old man’, but never just called him a man.
Adults would generally use actual adjectives, ‘male/female cat’ instead of ‘man/woman/boy/girl cat’