I had a similar experience this past weekend. My DS4 had a playdate at a local science museum with ND twin girls slightly older than him, and the differences were enough to make me think it might be time to talk to DS4 about giftedness. At the dinosaur exhibit, the girls were clearly struggling with the concept of extinction; my son excitedly chimed in with, "The birds that are alive today are descendants of dinosaurs." At a bug exhibit, after DS4 correctly pointed out the differences between the male and female of a certain species, the girls asked their parents what "female" means. The parents explained it in terms of "the mommy" and "the daddy," which sounded like babytalk compared to the conversations I'm used to having with my son. When the girls pointed to "little fishies" in a tank, my son correctly told them "Actually, that's a diving beetle." He wasn't trying to show off, just stating what he'd read right next to the exhibits moments before.
I'm struggling with how to tell him it might be best to keep his enthusiasm to himself. No one has ever told him he's "smart" or "gifted" and he assumes other kids his age can read, so he really has no clue. Luckily, the other parents on the playdate didn't understand half of what he said, so it wasn't a big deal, but I got increasingly nervous as the playdate went on and I realized just how big (and apparent) the gap really was.