What is This?

Recently, a member on a forum approached me to tell me about this Sandy Alomar Jr. promo he had found when buying a Ken Griffey Jr. promo.  He described it as a blank back version of Alomar's 1990 Classic Update card, but with a yellow border.  Not having ever heard of such a thing, I agreed to buy it.  Here it is:

And yes, the back is blank.  I have no idea what the story behind this card is, but I am very happy to add it to my collection.

For reference, here is the regular version:

So yeah, different-colored borders and a blank back.  This is a very intriguing oddball item.