From what I've read, his channel was never fully demonetized (specific videos maybe), they just removed him from the "google preferred" platform.

This platform allowed advertisers to place ads on specific high performing videos or target ads based on specific youtuber's videos. There is one maker channel I watch and it is weird to see a pre-roll ad for a welding company and at the end of the video they say, "thank's for watching, now on to Jimmy's video!"