Haha.. well, I honestly think it depends on the child. I know for me personally, I don't mind if my mom ever brings it up, and I didn't back then, either. I did feel a little awkward sometimes when she teased me about me and my "future girlfriend picking out china together" because I wasn't quite used to the concept myself and it just felt weird to be teased about something I felt so self-conscious about.. but teasing is different than if she ever had something genuinely serious to talk to me about.
I think if you say it casually, like.. "Hey, I was just thinking about something I said the other day when we talked, and I want to let you know I know your sexuality isn't a choice, I may have worded it poorly." I don't think that would be crowding.. crowding would probably be bringing it up
all the time and plastering the house in rainbow flags, lol.
But again, it really does depend on the child.. did he seem comfortable with himself when he told you, or did he seem nervous/unsure/insecure/uncomfortable? If he's uncomfortable talking about it, or uncomfortable with the idea he might be bi, it might be best to just let the topic go until he brings it up again. But if he was speaking freely and openly and sounded comfortable and sure, then I think you could bring it up without it causing trouble.