Would it be safe to say then, that Apilayer has simply acquired the trademarks and the domain name of an open-source project?

Edit: If the entire project is licensed under Apache License 2.0, what does acquiring the copyright give? The ability to change the license going forward?

And the copyright, dude. And literally what else is there? That's the project itself.

They probably also acquired the copyrights the seller held on the code, allowing them to use them as they see fit ( for example integrate them in products that have incompatible license requirements)

And copyright?