However, Satoshi did use an account on this forum, along with an email address. All connections to this forum logged his IP address/user-agent and other digital traces.
You can't do much with an IP address. It could be the IP address of a Tor exit node. Or perhaps another pro-anonymity protocol. Or VPN. Or maybe Satoshi just used to go on coffee-shops with free Wi-Fi to code or/and write forum posts. Or a combination of everything mentioned.
He probably just used Tor though. That's the safest approach.
By the way, Satoshi is not the only person in the cryptographic community who's remained anonymous. Monero's core development team is mostly consisted of anonymous people, like van Saberhagen and thankful_for_today. Today's anonymity protocols probably provide sufficient anonymity.