It simply means what it says. The first few leaders were simply in charge of everything like an owner, they made all major decisions themselves and told everyone else what the plan was, and each one did that job until they decided they didn't want to do it any longer and handed it off to the next leader. They were a dictator only in the literal sense that they dictated, not that they were tyrants.

They weren't literally an owner. That's why the "implicitly". Everyone was still only volunteers. But everyone volunteerily let them call all the shots.

Then later they developed a formal democratic structure and the leader is more of a coordinator than boss.

I assume the Ian Murdock (founder and Ian in DebIAN) transition to Bruce Perens, then Ian Jackson then annual project managers.