Popping up with no official announcement is definitely a surprise, though it's not the first time murmurs of Transformers: Fall of Cybertron coming to contemporary consoles were heard as the game was spotted on a Taiwanese ratings board for current-gen consoles back in June.
No mention is made of any new features in this release, so it's unclear if it's a remaster or a straight port. Given the lack of fanfare, my money's on the latter.
That's not inherently a bad thing though, as Transformers: Fall of Cybertron was fairly well-received. Eurogamer contributor Alec Meer called it "a good-hearted festival of a game about talking robots shooting and smashing each other" in his Transformers: Fall of Cybertron review.
In related news, today marks the 30th anniversary of The Transformers: The Movie. That explains Fall of Cybertron's surprise release.