If the bitcoin haven't moved from Satoshi's wallet there's a possibility the group behind Satoshi shared parts of private keys between them.
multisiig was not a thing in 2009-2010
there were no 'group' keys
secondly. satoshi was a single person with a single username
he talked and interacted and got help from other people. but they had their own names
like Hal. like Sirius
hal and sirius did not work physically in same room, building, neighbourhood as satoshi. they interacted over the internet