Well, I will state that Mojoman is in the habit of making himself look suspicious in general, so that certainly doesn't help things to start with. Most of it would come down to experience with playing the game, and playing with Mojoman.
But the odds of Mojoman being a Fake Cop and just happening to select the Real Cop for his his Fake Cop Claim are fairly low.
On the other hand, if Mojoman was the Real Cop, and he got an accurate report on a Mafia member, then Mafia would be forced to counterclaim his Real Report, and instead of their teammate possibly outing themselves by making a Fake Cop claim, it would make more sense for the player the Real Cop is stating is Mafia to make the Counter Claim.
Basically, there's a 33% chance of the first one happening in how this game turned out, 1 Cop out of 3 Town Players. While in the second scenario, it'll nearly always happen if the Cop gets a guilty result on Mafia.