From scum!DatSwan's point of view, either iguana is scum or town, and he knows this (I think technically SK is an option here? Not sure.)
If scum: Then he does not really want to dissect his partner's claim.
If town: Then he already knows that there is some reason for the claim, whatever that may be. So if he makes an argument that iguana's behaviour does not make sense as any town PR, then iguana just has to claim and it's likely that what he says will make sense. So really all this doesn't help mislynching town!iguana. And is scum!DatSwan wants to figure out what iguana's PR is, he's way more likely to do this in his QT.
I think you have a valid opinion, but I wonder how much of it is based off what you would do and how much is based off what I would do. I have never used my QT in that manner before. Everything I have to say I would say in thread, but put a town spin on it.
Do we even know if mafia have their own personal QTs this game? Most games I have been I think mafia have a shared QT and that is it. Looking at the rules I don't see any indication that this would be the case.
And I don't agree that iguana's explanation will just make sense and he will be given a pass for it. Maybe it will, maybe it won't. I think it an avenue for mafia to potentially explore.