Firstly, you're allowed to feel proud of your son. Navigating other parents is a skill you'll pick up quickly, humble is a good look that will get you and your son a long way, but it sounds like you've picked that up already.
If he continues to progress more quickly than his peer group, you'll have a few challenges to think carefully about. His 'difference' will become apparent to his friends, probably around year 3 or 4, and if he's got good teachers who help him and his friends navigate that difference, that will help. Keep an eye out for changing friendships at this stage. Maybe think about exposing him to out of school activities that involve a different peer group than his school friends, so he's got other social circles.
Absolutely agree with the advice to help him find activities that he finds more challenging and needs to work at. Not yet, but towards the end of primary age, keep an eye out for activities he shies away from, and think about why that might be. Definitely encourage some physical activities, ideally some team sports if you can.
Not one to worry about yet, but take a deep breath when you get to teenage years - and this may well be earlier than you expect. If your son is a curious, questioning type, you may find your every request and decision challenged - not through defiance or naughtiness, but a genuine desire to understand exactly how their ever expanding world works. Be prepared for every parenting inconsistency to be thrown back at you, and don't be afraid to admit mistakes and talk about the important balance of heart vs head.
Find something that can join you all together as a family - board games, music, geo caching, paddle boarding - something that brings everyone together on a level - and turn to it when times are challenging for any of you (especially your other child!).
It can be a bumpy ride at times, but having a kid who makes you wonder every day is a massive privilege. If you can, find other parents in a similar situation - being able to talk honestly without that feeling as if you're bragging is so helpful. And enjoy it (quietly, of course!)