Are there other places for friendships to form for him? DS8's best buddy is a neighbor boy, and he has friends from pre-K, soccer, Lego League, and other extracurriculars. Again, nontraditional, but he's happy with it. (We also have a school-for-homeschoolers that has a lot in common with what you're describing in the private school, only bigger, so that has helped socially. But all his best friends are from places other than his stint at public school. And all these friendships have lasted.)
You might just have to be more like a homeschooler in the way you handle his social life. If you meet someone at the park who seems like a potential friend, give out your phone number or e-mail. It's not always easy, and it's very much like dating in that you have to be prepared to ask and be rejected. But it does ultimately work out if you keep asking.
Of course, it's also possible to say that you'll join the small school IF (and only if) they have an elementary class. That's perfectly fair!
