You aren't just lying about one person's role as a fakeclaim mason, you're lying about two. That's two chances to get caught by something like a rolecop investigation, two chances to get vigged off, and god forbid there are
real
masons in the game those are two townies you've confirmed yourself as scum to. Hell, it's not at all unlikely for a coroner to be in a partial-reveal in this game. I'm not trying to say any of these circumstances are true for this game, just that there are too many unaccounted variables for scum to claim mason in this manner.
I can imagine scum-Baezu crumbing early and then fakeclaiming later in the game when his team has more information about the possibility of real masons in the game. However, a claim this early and this unprovoked does not feel like scum to me.