The copyright holder can change the license for new versions. Copyleft does not matter.

It does when there are many copyright holders, like famously in Linux.

You're right, but I am seeing other random Reddit posts that say Google has simply changed their development workflow/branching strategy, and that the claim from the OP is inaccurate.

At the moment we have 200+ upvotes on something that is very light on information, but heavy on confusion. I am just trying to understand what is going on.