Erm, no one got the Realta Nua Art as the mini-poster; the Realta Nua Art WAS the (digital screen) movie poster.
I was worried that I wasn't going to get a mini-poster (of the actual film poster) myself, but fortunately I stuck around long enough in the immediate vicinity (at least a few minutes past the short PV for Lost Butterfly) to encounter the theater employee handing out posters to theater goers. They meant to be ready to hand them out earlier (maybe as soon as people started leaving the screen?) but apparently the movie ended sooner than they thought.
Be sure to ask about it! (And even the first answer you get might not be a guarantee-- IIRC, when I asked about it when collecting my ticket, they seemed to think there weren't any 'goodies' to be distributed to film-goers.)
Was it this one?
If so, at least that is official promo material.
Maybe the one who put out the Realta Nua art as the theatrical promo art is using subliminal messaging to tell you to READ THE VN.