There IS a 1970 S quarter known struck on a 1900
Barber quarter, but it is in the same category as the 70 s struck over a 1941 Canadian quarter, just something a mint employee made and smuggled out of the Mint to sell for their personal profit, not a mint error, just a fraudulent item.
I can't see anything from this "enhanced" image. Shooting the picture through the proof set case doesn't help either, but I realize that unlike modern sets this one is not designed to be opened and reclosed.