Look at it with a loupe - can you see a difference in the surface of the metal at the line that breaks the grey from the copper ?
hmmm....looks like you might have a defective planchet error where the plating was wrong on the blank planchet. Tough to tell without the coin in hand. My guess would be though, that the grey section would be badly pitted if it had been dipped in anything acidic b/c of the strong reactive nature of zinc.
