Maybe. Either that or it's an attempt to frame Hubert, but other than the cypher itself, there isn't anything that traces back to him in it. And, if they were attempting to write something incriminating, why would they pick something that only he could read?

Hubert himself could easily have dismissed the evidence completely, especially if I hadn't been able to break it. He could have said that the note was something unrelated, since the two of them were communicating in it.