I apologize for the slight delay. I should first clarify that I think I understand your son's position in this. He sounds like he may just be a bit socially awkward right now and he will likely eventually grow out of it. Although this is not something that is likely to derail his life even if a criminal prosecution goes forward, he does not need the aggravation right now and you want to minimize the consequences to the extent possible.
Law enforcement always has a difficult job--they first have to decide if justice would be served by prosecuting a crime; they would then have to prove guilt beyond a reasonable doubt. Oftentimes, this cannot be done without the "cooperation" of the suspect. The best advice that anyone can give any suspect is to not cooperate with law enforcement whatsoever. If asked to participate in an investigation, the second best answer is "I respectfully XXXXX XXXXX participate except through legal counsel." The best answer is to say nothing at all.
It is difficult to gage with the information provided whether law enforcement would take any interest in this case in the first place, but if they do, I recommend that you watch this video
to understand your rights in this situation (follow link).
I should in conclusion warn you that law enforcement does not need to notify you before or during an interrogation of your child. It is important that your children know their right to not answer questions, even if they are being pressured by school officials or law enforcement to participate.
Let me know if further clarification is needed. Thank you.