agreed on the old injury. could have been from when he was a kit with mom (mom did it or siblings did it), or could have been from another chin he was housed with before you got him. or could have been a bit of a mishap with an ear tag. i wouldn't worry one bit about it at all.
agree with all of the above, it appears to be an old injury and it surely is nothing to worry about. I have a male that has the same issue..old injury, tore on top though...and he's perfectly fine.
our chin Raichin has a hole in his ear. at first that was how we could tell them apart!! lol but it doesn't seem to bother him. he had it when we first got him.