Hi, Learningmom-- with those social quirks, PDD plus gifted is possible, though as others note there are plenty of undiagnosed quirky gifted people too.
I'd pursue it just so you know for sure. Because the symptoms are distressing some of the time, and possibly in his way in having good social relationships, addressing them is a good idea. The special interest conversation gets less cute as they grow up.
If you do get the dx it will buy you some good advice about how you as his teacher should handle the meltdowns and work on expanding the social skills.
Dee
