Autistic boy smells girls hair, girl yells at him, teacher reprimands him? Is this right?

This boy probably has an IEP (Individualized Education Program) that includes special disciplinary actions for when he misbehaves. So it could be the teacher was supposed to handle it differently. But teachers face a lot of challenges when it comes to the mainstreaming of special needs students and maybe this one doesn't have the support he/she needs to manage this child. What IS likely is that unless he stops infringing on the personal space of other students he'll eventually be taken out of this class and put into one more befitting his lack of self control.

Autistic or not, he needs to be taught personal space/boundaries.

Yes, it's right. Smelling someone else's hair or anything else that involves that kind of close, bodily intimacy is NOT acceptable unless you're invited to do so, or you're in a relationship with that person. As an autistic boy, you might not have known that. Now you do.

If someone goes up and grabs my face without me knowing i would probably hit them. He’s lucky she didn’t slap him.

He did something wrong. He was yelled at by the girl. The teacher told him to leave her alone. Is he suppose to get a Get out of Jail Free card because of his autism? Nope. He needs to learn proper behavior just like everyone else. The fact he is in a classroom with other kids means his autism is not all that bad. Teacher was right, kid was wrong.