How exactly?
Nobody can say that the mobile apps are open markets anymore, the app would have been rejected on the appstore from the start and is now removed from the play store. Effectively the distribution of this app on mobile devices is in practice impossible now.
It also highlights the similar review process and lack of differentiating competitive factor between those two stores. They aren't interchangeable like supermarkets are.
We knew all of that already but I like that Beeper mini made it obvious enough that the PR lies of both companies cannot work here.
I don't know what the legal status of the protocol per se is, but I don't think anyone thought that you would be allowed to utilize Apple's iMessage servers for your own app.
Apple could have said that no other clients really even tried before this case and it would have been true. And that will make a difference in the next antitrust lawsuit, that's one less argument Apple can use to defend themselves.
I'm sure most developers expected them to behave like this but now there's a factual proof valid even outside of our tech developers little circle, it's not just speculation.