First thing to say is Congrats to your DS.
Our DD did this last year, so I had a trawl around at the time. This is what I picked up.
I believe it's top 1-2% get all 17. Older girls fair better, younger boys worse in the scale.
Has the teacher over egged it? I read through some opinions, and the consensus seemed to be that there's no reason for a teacher to, and some reasons not to (it sets the targets for KS2, so the best they can do is remain on par with your DS), also the criteria is pretty binary - have they been seen doing X. Many schools just don't have the time to gather all the evidence.
Is he G&T, - too early to say, I took a look into the message board on this site for G&T, and ran screaming. I think it's more about single subject excellence, if DS is not knocking out original compositions or the like, then I'd suggested not going there, same with tutors, would seem to far too early.
So.. what else.. it's a little annoying, not mentioning it in the playground is pretty obvious, but then it's difficult not being able to broach the subject, to get a comparison, is DD far ahead than other kids, or just a little? No idea.
In the end we settled on carrying on as we were, trying to engage her curiosity, praising effort over attainment, being kind - that sort of thing. Personally I think that kids switch on to school at different times, that your's has switched on early is great, and in a couple of years the picture will become clearer, as he gets more competition in class, and as particular talents emerge.