advice please?

My 10 y old son has high functioning autism, adhd and spd, I've been noticing he has been talking about the same class mate frequently at home and underlying telling me that he's not doing the right things to other kids (it seems to me he's very close to a bully), but my son keeps hanging with him in school and then comes home to report him... I've tried my best to explain to him that he should just not interact with him if it makes him uncomfortable and always report to a grown up, if he sees something is wrong.

I had already asked the sen to please sit them in different tables etc, as that boy was disrupting his concentration in class. Yesterday he came home with a swollen bloodshot eye... i didn't receive a call from school, there was no slip in his bag saying what had happen, so i asked him, and was told he accidentally flipped his pencil under the table as he was shaking it between his fingers (to cope in class) and it hit that boys leg, my son said sorry, went under the table to pick his pencil and  when he was coming up he saw the boy with a pen cap positioned in his fingers like in a sling shot way, and the boy threw it at his face hitting him in the middle of his eye. The teacher heard him scream and cry and asked what had happened, to that my son got silent and very shy( as he usually gets when he doesn't understand what just happened and why!) so she asked him if he wanted to talk about it and he said no, and it was left like that. i asked my son if he said sorry and he said that his answer was smiling  " sorry mates didn't take my meds this morning!"

I was fuming, i still am... i went to speak to the headmaster and am waiting for feedback on Monday... but my question is: am i over reacting? Im always very weary of talking to school staff because all they say is that my son in such a wonderful compassionate and caring  boy to see if they can just leave it as - mum took the compliment and is now quiet because we care and know him... or trying to tell me im just very anxious about it... always fobbing me off... so i try and do what i can at home according to what im told by my son, guiding him and helping him understand reaction, social expressions, behaviours, that he unfortunately lacks the skills to understand... 

Sorry about the long post, any advice welcome