It looks to me that the frame is drilled slightly off center, making the barrel shank sit inside the frame slightly to the left (as viewed from a shooting position from the rear). Since the barrel sits inside the frame slightly left, the barrel lines will not line up with the center of the frame lines. To correct for this, I'd wager that the rear sight would need to be drifted slightly to the left.

This is not a case of canted sight. It is a case of a barrel shank drilled off center inside the frame.