I think it is a random offer, probably based on how active we are on the site. I'm really active betting in the last few days although I do wager few BTC only. I was so surprised as well when she (Irena) offered me 25% rakeback, absolutely I accept the offer because it is really good offer to be missed. Maybe next time other players including you will be offered the same thing or even higher rakeback.
So all it took was to ask support to see if you have been using the site often enough to have it applied.