If you need Android Auto, the closest thing you’ll get is LineageOS with some sort of GApps, but those are far from the “privacy and security first” goals of GrapheneOS.
If you are looking for something private/“FOSS-focused” and don’t need Android Auto, I like CalyxOS a lot, and have heard good things about DivestOS.
His linktr.ee from his official website links to that account. So it’s official.
I think the question is: is it actually him using the account, or is it a social media manager?