Do you believe it when people say never trust a person if your dog doesn't like them?

My dog was terrified of my new boyfriend. (Now ex. We were together 3 months) He (my dog) went from being with me all the time to never coming downstairs. And having tail between his legs. My ex swears he never done anything to him. My dog is a small terrier breed and yes quite nervous. But he usually likes a person after he has met them 2 or 3 times. This was first boyfriend I've ever had though with my dog. My nan always used to say though to never trust a person if animals don't like them. Do you think this is true?

Do you believe it when people say never trust a person if your dog doesn't like them?
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