My nuerotypical and autistic son did this but both outgrew it after some years. My autistic son spat a lot but only does sometimes now. Now he likes to pour out cups.

My daughter would gag and vomit after eating. She'd run from the table and do that. I narrowed it down to texture of bread. Maybe it's a sensory to texture, taste, etc ?

How old is your son. My son has a spitting issue too. He has to carry a spit cup wherever he goes. I think it's common with Autistic kids. My son doesn't spit food but the spitting issue has been going on for some time.