"Sleepy Bill Burns, the man who helped fix the 1919 World Series, could pitch with either arm, but did so only for exhibitions. He pitched lefthanded in games, then would work out righthanded between starts. He said that kept him in better shape than most pitchers."
http://cpcbaseballtrivia.blogspot.com/
Seems the glove was not an artist error but a nod to the fact that Burns pitched righthanded in exhibitions and between starts. So could be an ambidextrous glove as Michael said, or intentionally "wrong" glove to emphasize this quirk of Burns.