Really, I don't see how Originals would have slipped so easily.
I'm not sure how night action PMs work with the conversation system but I think everyone submits their night action within the same Role PM conversation, right? At least that's what I do. If so, ALIT would have seen the green letters again when submitting his night action, in case he did forget.
If he's Mafia he wouldn't need to look at his role PM again. All night actions would be done through the QT. And if he was VT, he should be able to tell us the exact wording of the green words if
@Jamie allows
Even without that, ALIT noticed the wording "Original Mason". I understand being taken aback from the wording at first but having time to think about it enough to bring it up, yet still not connect the two? I've never seen "Original" any-role before in an Mafia game here. That would cause people to wonder what on Earth that means. So coming to the conclusion that it means normal Mason but not connecting the town name. I don't find that too likely.
I would attack him but in case most people belive his reason, I'd suggest keeping this incident in mind through out the game.