Your son has/had definite symptoms of being on the autistic spectrum. I can't diagnose, but the running and freaking out in crowds, and his happily staying out of all things social, do sound like it. Really, some might disagree with me, but I wouldn't even bother to go have him diagnosed because you all are fine and he is fine and he is finding his way in life and has his niche.
There is no good treatment anyway. I am glad my son was diagnosed because it finally meant that it "wasn't anything I did wrong." However, there are no drugs to fix it (and I am glad), and "social skills classes" are of no use as I have found. Unless possibly your child happened to find a like-minded soul for a buddy in one of these classes. Mine was always the most highly-functioning. But figuring out the right behaviors to use in the lab with other auties si very different anyway from navigating the real world with the rest of the human population!
So keep doing what you are doing and make his childhood happy. Hearing on this thread how many people had miserable childhoods reminds me why I decided to homeschool my son.
I don't like to think of him as a diagnosis. He is my son. He is just fine the way he is.
That's just it --- he has the symptoms but he has no real problem and by age 14 now can handle the crowd situation even if there actually might have been a neurological response he couldn't control at age 8 or 10 --- and I do think some of his stranger responses were neurological but not serious because they were partly due to an immature nervous system. Some of it was maturity but some was just letting him be --- at family reunions and gatherings he would stay at the edge --- not really interacting with cousins but able to join in on activities like hiking and exploring even though he's just as happy to do that alone. I guess if was desperate for friends or unhappy I'd be worried. Even the teachers would say it is just that his mind is at some different level --- he doesn't relate to the others because they don't share his obsessions but I think as he gets older he might meet others like himself if he gets into the right field of work and then I would expect he'll socialize somewhat or have friends. Or else he'll do what he's doing now --- limiting his social life to within the family and animal pets. He saw Seabiscuit and so is trying to communicate with horses like the old horse trainer and has now trained his horse to follow him around with no lead rope or halter. To me that is being social but just in a somewhat different way.
I actually think those who fit in with the crowd easily often have the more serious problems because they're steered too much by what others think. They may be popular and seem very normal because they have so many friends but from what I see of all the piercings and tattoes, teen drinking and drugging, I'd be more worried about a crowd pleaser than a loner.