I don't know anything about Ruby so forgive my ignorance. As I understand it there were repos required to run the RubyGems Service. This was of interest to major corporate players. Instead of removing the original authors, why didn't they just fork the requirements?
And wouldn't that constitute a violation of ownership? Or did the authors wave that away by joining the respective GitHub org in the first place?
Basically, yes.
It is murkier as the involvement of some of the original creators in Ruby Central is there, so there are claims to being the original copyright holder applicable to some areas by a very small number of individuals, none of which who are the newly added maintainers, or Ruby Central as a whole entity.