The way I understood it creatine by itself doesn't promote muscle gain all that much. It's the fact that you can potentially do one to three more reps which does. But that still means you have to do the reps. https://leangains.com/supplements-you-might-actually-find-us...
This has been known for ~15 years. I'm not sure what this study thought it was debunking.
Note that this link is not the study! The published paper makes much more specific claims.