I find people are generally like that with all small animals that are likely (in their minds) to nip. Grown men that are petrified of holding a hamster, for example! Conversely, they are quite happy to thrust their hands or arms into mouths full of sharp teeth with a dog. As has been pointed out, Parrots are an unknown quantity for many and people really don't know what to expect.
My brother, when he met Monkey my Senegal for the first time had to ask what the most amount of damage he could receive from a bite. I, of course, said he'd take my brother's arm off but people really don't know - they just see that beak and are naturally a bit apprehensive.