I have been a dedicated minor league collector for 30+ years and have been aware of this "card" for a long time...and it is not real.
Well, I mean sure it's obviously real in that it exists and has the look and feel of a baseball card, but...
-it isn't from 1980
-wasn't produced/released by the Greensboro Hornets
-isn't officially licensed
SCD has a great book called The Standard Catalogue of Minor League Baseball Cards (published in 2000 and edited by Bob Lemke) and it includes a listing for this card which has an image of the front and states:
“1980” Don Mattingly Greensboro Hornets
Unauthorized issue produced in the late 1980s; no collector value.
(Yes, it actually has quotes around the year.)
I’ve seen these pop up occasionally on eBay and can recall seeing one sell for over $400 several years back. I had exchanged emails with Mr. Lemke about a few minor league sets and shot him a message with the link to the completed Mattingly. His reply was simply, “How unfortunate for the buyer.”
I am beyond appaulded at the current listing on eBay...and hated seeing that the seller apparently suckered someone into purchasing a copy recently.
While the card isn’t real, it does at least seem to have been printed in far fewer quantities than other minor league fakes/counterfeits (ex: 1985 McGwire Modesto, 1988 Griffey San Bernardino and a Mattingly B&W Columbus Clippers card that has the TCMA design from 1985.)
But regardless of print run, it’s still a fake.