*It's been a few years since this happened, so I'll try to describe it as best I can. Looking back, I would say the guy in this situation was most likely autistic, just curious what other people's take on it might be*
Some years ago, we had a mother and son who were semi-regular visitors at the library, and the son definitely had what you might call "hidden disabilities". The mom would come in to use one of the computers, and her son would spend the entire time standing rigidly behind her, or he would stand in a corner........I don't think he ever made eye contact or spoke to anyone. They must have lived in the area, because he "escaped" from the house, and went to the library.......I remember the mom had to take him out the staff entrance because he would not/refused to go out the public doors, and that he had a really stiff/robotic/quick way of walking.