Here's a link to the story:

http://borosny.blogspot.com/2012/02/baseball-card-story-from-mark-grant.html

I received an autograph from Mark Grant today (2/28/2017) on this card and he told me the story of it. He said that he was not pitching that day and was asked to take this picture. He didn't have his glove so he asked Tony Gwynn if he could use his glove. If you look real close at the photo you can see the number 19 on the glove just below emblem on the thumb portion.

Having the glove on his left hand is not an error but a joke by Grant.