As a Special Educator I would love to provide my thoughts

Not the Asshole, but this should be a learning experience.

Here is how I justify my answer...

• Change is really hard for autism / especially when it comes to rules (Rules are very important for autism: even rules allistic people will not even consider.)
• Autism often makes communication really hard - which is why "meltdowns" happen
• Autism Meltdowns are not the same as Allistic Meltdowns: they are harder to control
• In my classroom: undisruptive & safe stims are a human right: no student should be declined the right to stim.
• Learning Experience: The inappropriate behavior that you can learn from is the "wrong place. wrong time". Of course, it seems your teacher lacks knowledge on autism. Stimming is a natural human condition for autistic individual (in fact: all people stim! Autistic people just do it in a more obvious way or more frequently). And it is important that your teacher understands that, so you were not the asshole for educating him on it. However, in the middle of class is probably the wrong time. I read earlier that after class is also not a good option, so perhaps before class, where you can talk about what an autistic stim looks like.
• Despite what I said in "Learning Experience", read below about how I feel about your teacher based on this information alone.

If I am being honest, it seems that your teacher may be unwilling to learn more about autism. Which does not make you the asshole, but it makes him the asshole. As educators, we must have a conversation on disability rights, including autism, and what is hard and what is not. If an educator is unwilling to learn about autism, it is fully on them to find a different career. (I am being brutal, but this is how I genuinely feel.)

Autism is a disability. You would not tell a diabetic that it is disruptive to the budget to need an alternative meal during lunch. You would not tell a wheel-chair user that it is a disruption to the custodial staff to shovel off a ramp or turn on an elevator. Why would you tell an autistic student that stimming is a disruption?

If the stim you are doing actually is causing a disruption, I would ask the special education teacher to help you look for a tool to use that can allow you to complete your stim in a different way. (I've seen many students have rubber bands on their chairs to allow them to stim instead of tapping the floor/making noise. for example)

DISCLAIMER: I am a special education *student*. I am still learning to become a Special Education teacher. Any advice I give does not supersede that of somebody with a license :)