I assume your friend tried a patch dot or scotch tape on his left shooting lense. Some of the top skeet shooters in the country patches their left eye. It just eliminates a lot of trouble with the right eye.
My skeet coach is blind in his right eye. He had a stroke 7 years ago and the right eye went away. He still shoots right handed left eye, but his leads on some of the birds were crazy!!! He had to lead like 7 feet for a high 4 I think. Anyway, the point is shooting left eye right hand is no bid deal.