Here's what I'm thinking.
Ichi was the first person to actually claim a PR. If he is scum, then the add on is Traitor Knows Mafia/SK.
If this is the case, then it's reasonable to assume that Ichi is the Traitor, since he would then have the most information and be in the best position to make a logical claim.
If Ichi was the Traitor, then he would know that we have either Column 3 or Row 3.
If we have Column 3, Psychologist is a believable claim since from a Neutral point of view with the other claims, we could have Row 4.
But if we have Row 3, there is in fact no logical fake claim, and a Psychologist claim would quickly be found out against the three real claims.
If he was instead the SK, he would know we have either Column 2, Column 3 or Row 1. This would make Psychologist a reasonable claim for scum trying to mess up ICs, but not so good for a SK trying to stay alive.
So if Ichi is scum then he didn't have enough information to know that his claim wouldn't immediately be caught out.
If, on the other hand, silver is scum and knew that the Mafia knew the Traitor, then he'd know we have either Row 4 or Column 2, neither of which would immediately out a fakeclaimed JK.
In summary, Ichi didn't have enough information to make a safe (at least safe enough to not be immediately outed) fakeclaim, while silver did.
Vote: silverspawn