[BugsJustFindMe]

> top of the right mirror is very slightly curved, indicating the perspective correction of panorama mode.

Straight lines are actually always curved in wide angle photos (you can tell because of the exaggeratedly stretched corners) unless you perfectly correct for it. It's called radial distortion and is a natural property of lens projection. This is not on its own a sign of stitching, just imperfect calibration.

Anyway, I also believe this was a pano shot, but a curve isn't real evidence of that.