Foil Avacyn confusion

Hello all. I have recently purchased a foil Archangel Avacyn and just received it in the mail today. Turns out I bought one that was a pre-release or some kinda promo as it is still in the factory clear plastic and is dated in gold 2-3 April 2016.

I didn't attend pre-release for this set, and I don't remember hearing or seeing any promos at my LGS for buy-a-box or anything....so can anyone tell me how they got their's? Was it a simple promo for buying product or was this seeded in the pre-release box's? Any input is appreciated, thank you.