OK, this may not be an issue at all, but fwiw - have you had his vision tested? Our dd who is now 11 had severe anxiety as a 3-4 year old when we took her to new places or to large rooms, or to noisy places, or to ... you get the point. We couldn't take her anywhere without extremely severe meltdowns, but she was a-ok happy at home with no obvious anxieties. We eventually consulted with a psychiatrist who attributed it to SPD who sent us on to OT for the SPD, dd went through listening therapy which seemed to help some, but she still was anxious starting school when she went to kindergarten, took most of the fall semester to adjust to being there, finally got the hang of it and seemed to be ok, then fell apart when she had to return after Christmas break. It wasn't until 2 years later, 2nd grade, when she was having a tough time learning to read and reading from the board that a neuropsychologist figured out the not-so-obvious for us - she couldn't see clearly!
Anyway, that doesn't mean your ds is having vision issues - but that there may be something physical going on that your ds has been able to become comfortable with at home and can compensate for but when he's in new situations, or places outside your home, he hasn't had time to be able to get comfy with them and figure out how to cope. Vision might be worth checking. A regular eye exam didn't catch our dd's challenge - she had 20/20 vision in each eye (individually) but her eyes didn't track together at all and most of the time she was either seeing double or one eye was completely shutting off to avoid double vision, which then meant she had no depth perception.
Best wishes,
polarbear
ps - one of the things our dd did as a toddler and preschooler was to avoid eye contact when people were speaking to her. She eventually would look directly at us (her parents) once we started teaching her explicitly to look at us. We had some concerns for awhile that some of her behaviors might be autistic, and she also appeared to be ADHD (with the H for hyperactive emphasized).... but the lack of eye contact and a lot of her fidgeting etc were actually due to the vision issues.
