Well, Muugen seemed confident he could pass himself off as a genuine candidate, given his initial responses. So he might have made an error in his calculations. I also forgot to mention we could only manage to track down two people who voted for him.
If I am mafia, the ideal situation is to have a member attract positive attention legitimately and bolster that. That's the best case scenario. Some have proposed that the mafia could put lemons on the council as well, but the problem with that argument is that it eats into the mafias collective vote power to put a townie on there. Furthermore, given the games size, it's likely we have splintered scum factions, so while they have good leverage idk if they can afford to waste it like that.
Importantly if you propose Muugen is being set up, that concedes that scum have an agenda to putting him there, and that's at least worth discussion. As it stands, it seems most likely he didn't earn his seat legitimately.