Yeah, Roman is the canonical "sole" killer. But this scene specifically was shot with the intent that there were 2 killers present, this scene makes it most obvious. You can search "Scream 3 - Second Killer" if you wish to know more. I doubt he could loop behind it, we don't even know if that closet can be entered that way. By the time Sid ran to the door, Ghostface seemingly had just gotten up. He wouldn't have possibly made it there with such speed, and we also don't know if that room had a back entrance, so i'm iffy on this claim.
Here if you want more proof:
Angelina Tyler 2nd Killer.