Because you are a big heat signature. Your face is a big bright, uncovered object to them. Remember they see heat. Ever see the moive "Predator"? Thats kind of what you look like to them.
I think it shouldn't come as a surprise when any baby snake strikes if you put something close to its face. With boids, it should pretty much be expected if it's something warm like your hand or face. They're new, small, and very nervous about the world, and to them you're a big monster that might try to eat them. So be gentle with your snake and try not to put anything near its face. It startles them, and it even startles some of my full-grown snakes to have any object suddenly put in their faces.
It shouldnt be normal... I agree with the heat target concept but that doesnt mean it should lunge at you. You asked for 'normal', so no its not. Normal red tails wouldnt hurt a fly. But of course some snakes are defensive, or plain hungry. But theyd have to be REALLY hungry lol. Sure you didnt touch a mouse then touch for face or something?
I touched noses with the nature centers common snapper and all he did was give me a WTF look lol! And its fun to do it with hognoses lol whenever you push their snout they kinda wiggle it away its so cute xD