[globular-toast]

You can buy the copyright from the copyright holder(s). That seems quite straightforward if the holder is a single entity, like with Qt, for example. If it's multiple entities, as with Audacity, then in theory it's no different, but practically speaking I'm not sure how they have done this.

[Conan_Kudo]

They probably hired the main developers and have the copyrights for their work transferred to them. In practice, it has no meaningful impact since relicensing is (nearly) impossible due to the distributed copyright among all contributors of Audacity (which is a good thing!).

[globular-toast]

Then "Main Audacity developers hired by Muse Group" seems like a sensible headline. I'm not sure why they went with this headline. Maybe they sold it to their bosses in simple terms like "we're acquiring Audacity"?