Glass Chip, How Did That Happen?

I found a tiny chip of glass sitting on the dial on this watch.  It appears to have come off the inside of the edge of the crystal.  Strange...  It's barely visible.  There's no sign at all of any injury to the watch or case.

This is an Elgin grade 82, 13 jewel version, made about 1885.  It;s a G. M. Wheeler movement.