I didn't think about it but a scratch could be possible. He was in a tank with a ridiculous amount of flow for a several hours.Or it could just be a scratch. You will know in a few days as fish fins and scratches heal extremely quick.
Glad the Purple Tang is good to go, I have one in my tank.
Purple tangs have always been one of my favorite fish, but in my years in the hobby this is the first one I've ever gotten.