Is animals not like a new Dom a red flag?

Okay I know this is kind of a silly question but hear me out.

My little sister is also into kink an D/s. Guess it runs in the fam. She brought home this new soft dom she's been seeing and all three of the cats hate him. They won't go anywhere near the dude, hiss at him, swipe at him. And these are super friendly kitties! I feel like it's a red flag if animals don't like someone. What about yall?

I'm I being an overprotective sis?