There are two ways I can think of. Sometimes, at trading events, Disney puts things on the boards that haven't been released yet. Or high level managers have access to "the good stuff." If the release got cancelled the AP and PP versions could still have been within Disney's circulation. I notice in the very left, bottom corner is a PP. That means Pre-Production. Also, auction lots at the big Epcot pin event sometimes include pins that were never released.
The pin was made, but not released, and then the factory sold it, not authorized by Disney. This is where things get tricky. Normally, pins direct from the factory are not wanted, but unreleased stuff provides a conundrum. Think about coins, stamps, or other collectibles the "money" is in the stuff that was never sold and meant to be destroyed. However, usually there is more than one pin, and so somebody else will be selling it, or put it on Pinpics or something.
Artist Choice pins are their own series. Originally, they were marked by a pencil & paintbrush, but the last ones that were sold had a round logo like the one on this pin. So, as someone who would if she would have thought more about it earlier would have tried to collect all the "Artist Choice" pins, it's a very cool pin.
Finally, Pinpics is not perfect. Pins do get missed from the database. Everyone else is sitting around waiting for someone else to add it. So it is possible that this was released at a pin trading event and whoever added the catalog of pins accidentally skipped it. Or the listing got accidentally deleted in moderation or something. I will try to take a look back at events that happened in 2009 and see if anything pops up.
I thought of another way. Artists, I think may have an option to get copies of their pins (especially, AP or PP versions. That's why they exist so the artist can verify the work). It may be possible the artist had one / several and then sold them for whatever reason.