That’s interesting. I now believe that is what happened here: that the mortise hole was drilled at a slightly off-angle. I DO believe that the tenon is perpendicular to the stem face. But the mortise hole is not perfectly perpendicular to the shank face.
100% yes.
It's basically impossible to make a "crooked tenon" even if you want to because of how Spinny Tools work. (heat and bend afterward, yes, but cut and have it be crooked? No)
Hand drilling a dead-square mortise, on the other hand, isn't possible. Close with practice, yes, but not spot-on.