I have recently noticed that I have a huge asymmetry in the cross body shoulder stretch. In particular, when stretching the left arm, I can push it to be almost parallel, to my body, while with my right arm I can't, and it stops at a 30 degrees angles with the body, because it seems the pectoral muscles on that side gets on the way. Can it be because I'm more tight on the pectoral on that side of the body?
If something blocks particular move, I usually feel what that is. I mean is it because of joint, or muscle, or something is on the way - like other muscle. It hard to tell, and your picture do not help. ;)
If you are right handed, then your idea is more possible.
Do you have pain? Please do some tests, for your shoulders. To see if everything is OK.