Well, I wouldn't want to diagnose your son but that sounds more like a social phobia or anxiety type of problem than ASD but, given his physical reaction, I can see how that would get classified as ASD. Also, he may have "grown out" of the more severe ASD problems - it's not unknown for that to happen.
Perhaps he would be considered to be "on the spectrum" - which means he displays some characteristic ASD behaviors or the ASD behaviors are sub-clinical in severity but overall he does not have enough ASD features to meet criteria for Autism, Asperger's or PDD-NOS.
And it could be classified as a tic (sudden, usually repetitive, non-rhythmic, stereotyped motor movement). I'm no expert but if he perceives it as an involuntary reaction under stress it may fit under that category of movement disorders. Especially if he has other behaviors that might be tics or problems with movement like crossing the midline vertically or horizontally.
Patricia
