These.
I have met friendly and unfriendly dogs of various breeds. When I was a child with various door-to-door tasks (Boy Scouts collecting donations, subscription stuff, etc.) I would encounter people’s dogs. If not for some strong chains, some very aggressive dogs would have bitten me. For just walking up.
This can lead to a misunderstanding when I see someone else’s dog which may be very calm and relaxed and would never bite anyone, but looks exactly the same as the other dog which was trying to bite me. Same breed, same coloration, same ears, same eyes, SAME TEETH!
I don’t know what set the other dog off. But something did. And the same thing (or something different) might set this dog off. It could happen, and I don’t know what it might be. Someone inexperienced with dogs will have that fear that something they don’t know about will set a dog off.
They’re wondering, “Is it don’t show fear?” “Back away slowly, don’t make eye contact?” “Climb the nearest tree?” “Run faster than your friends?” “Let them bite your arm so they don’t get your throat???”
Pretend you’re someone who’s never been around a horse, but you’ve heard or seen in movies that they can kick behind them and hurt/kill someone … the first time you’re near a horse, do you walk behind it? Of course, there’s safe ways and unsafe ways to approach the back of a horse, but if you don’t know which ways are safe and which ways aren’t, the best way might be to give the back of the horse a wide berth.
Same logic might apply to dogs. A person who’s only experienced a tiny dog in their childhood might, upon meeting someone’s aggressive looking rottweiler, pit bull, or large shepherd might be intimidated upon first meeting it. Heck, someone who saw Cujo might meet a St. Bernard and freak out…
As far as fear clouding the ability to calculate one - people who seriously fear flying might prefer to drive, take a train, or take a bus rather than fly, even though someone can show statistics it’s safer. I’m sure there are plenty of other examples of this type of behavior.