First of all, are you sure the run is fake? Have you tried discussing this with the runner? There could be a perfectly normal explanation for any discrepancies and I’m sure they would appreciate you bringing up your concerns with them or the broader community before you label them as a cheater to the entire site.

EDIT: Deleted post by OP.

Just checked the leaderboard and the run. This game uses in game time as the primary timing method. At the end of this run you can see the in game time is 5:45. The video is much longer, presumably because of how the IGT works. So yeah. That's that resolved.