I think you're missing some key points

We typically threaten to lynch people for producing WIFOMs or claiming vanilla without pressure on day 1. Primarily to prevent people for doing it. If given a WIFOM scenario that has someone as 50/50 of being guilty, on day 1, we kill them, hands down pretty much every single time. It why I actually avoid WIFOMs involving myself whenever possible, in both alignments. Way I see it, why hand someone two glasses, one poisoned? Not a really good tactic. Makes a great delaying maneuver if you're trying to distract them while your sniper lines up a headshot, so to speak, otherwise no, never flip an unloaded coin if you don't have to. We also have a very strong 'you lie, you die' policy, which is one of the reasons I virtually never lie about anything beside my alignment if I can possibly avoid it. When you suggest we might be in an all vanilla game, I for one view that as an open admission of vanilla-dom while trying to technically avoid actually saying it, and worse, bringing up the option that might encourage others to claim vanilla too.

Well, theoretically, it could also indicate that it is just townies vs. mafia goons. It would be a good way for the mod to hide that.

to mafiascum wiki. Note that we have 12 players here in this game.

Yeah maybe not then, but it is a possibility. The townies wouldn't know if they are in one or not, but the mafia probably would (based on their roles).