What I've heard a while back is that right-hand or left-hand has to do with not crossing the blade with your arms.
With a right-hand saw, your right hand is on the main grip, left hand on the aux grip, and blade is positioned to the right of all that. It's similar with a left-hand saw.
But when a righty uses a left-handed saw, the right hand is on the main grip, left hand is on the aux handle, and your left arm crosses over the blade. The blade is aligned between your right hand and your body. Yes, the cut line is more visible, but it places the blade inside your arms, rather than outside.
In such a position, if your left hand holds a workpiece and your right holds the main grip, you could in theory accidentally put the blade in contact with your left hand.