First, please know you’re not alone. I completely identify with being a parent with a child who has a hard time with social cues.
Have you spoken to your son to find out what gave him that indication? I find that with my son I cannot assume that he should have known the cues. You may have to help him to break down each part of the actions to see if you can help guide him.
It’s very easy in kids with ADHD to have challenges with Executive Functioning which is part of what manages these social skills in neurotypical children. Here’s a link that you can start with that may lead to other ideas for you: Executive Functioning.
If you can afford it, I would suggest getting your own evaluation done. Though some schools are great, they are also dealing with a large number of students with needs and sometimes cannot be as thorough as a private evaluation can be.
Hope this helps!