Yes, this is a brand new album. No, it's not B-Sides. Albarn and Hewlett pointed out that they didn't want to wait a bunch of more years for a new album because they're getting old, they're getting back on the same page and they'd rather ride the high while they still can.
This seems like a conscious effort on part of the both of them to get back to some of the simplicity of the Gorillaz. Back when the only regular collaborator they really had was Del, when it was just a cartoon band making some good music. Putting together an album the likes of Plastic Beach and Humanz is a monumental effort of hundreds of collaborators. They're a fantastic coalescence of talent but stuff like that only really comes together in a "right place / right time" kind of fashion and usually ends with way too many years between music.
If Albarn and Hewlett are in the mood right now where they want to just pump out some good music and build the world they have, I'm all for it.