Not sure why he has to tell you what the name reminds him of. He could just keep quiet.

Other than that I am not sure how I’d feel. If it was both of yours child and he wanted to name them late fiancées name then it would be a no no. But it’s his cat and you do not live together so I guess he could name his cat what he wants. I just don’t think he had to tell you about fiancés cat