From SA Mafia Wiki
Post hoc, ergo propter hoc means "After this, therefore because of this." It refers to someone conflating two events as being connected simply because one occurred before another. In the context of a Mafia game, it usually involves night actions: say a Tracker follows Player A to Player B one night, and then the next morning Player B is fipped as the nightkill. If the Tracker believes A killed B for no reason other than believing A targeted B the night B died, then the Tracker is engaging in the Post hoc fallacy. Just because A targeted B during the night does not mean A was performing a nightkill; A could be another Power Role, the Tracker could have been Busdriven, etc.