The ePub spec does not specify any specific DRM implementation, just how to apply one. Choosing a different one than Adobe's doesn't make it "not an ePub", any more than using Adobe's makes it "not an ePub".
So they add crap into an epub, making it an epub+(rubbish-that-will-make-your-life-difficult-in-the-long-run). How is that not almost an epub then?