Let's ignore that Janus is mostly self-preservation at this point rather than 'Deceit'
Everyone seems to think Janus is a really bad liar. For example: when he imitated Logan, he wore the wrong tie, said 'lies,' and used an idiom.
But then when Virgil showed up, he snapped at him for 'ruining his dramatic entrance.' He totally expected them to figure him out. He planned it, because he's too Extra to just show up as himself.
More proof:
Selfishness vs Selflessness redux. Nobody knew he'd replaced Logan until he told them. He had them completely fooled, as well as the majority of the viewers, I'm sure.
Selfishness vs Selflessness. Yeah, we all knew Patton was off, but how many of us actually figured out it wasn't Patton?
Virgil knew, because he knows both Patton and Janus seemingly well, but considering the Janus/Virgil dynamic, I am near certain he did that on purpose.
Would Patton have messed up referencing famous philosophers? Yes. Did Janus know that? Most likely. However, his knowledge impressed Logan, and Janus wanted the other sides to take his side. He probably figured if he got Logic on his side everyone else would follow but then realized how little they listen to Logic.
Every bit he did that wasn't exactly Patton-like, I am certain there was a clear, intentional reason behind it, even if it was just to annoy Virgil by letting him be even more sure it was actually Janus. 'Friendo'? Come on. Patton's literally the dad character. There's no way that wasn't intentional.
"Is C!Thomas capable of such deception?" you ask, because he is a bean.
Yes. No, C!Thomas doesn't lie on a regular basis or anything. But he. Is. An. Actor. Actors can lie. They can deceive.
Just because he only does it on the stage, doesn't mean his sides can't use that skill whenever. I also believe his skills in acting have a lot to do with Janus in addition to the Creativitwins but that's for another time