Dang it was real...
You must constantly move back and forth between the Room with the ENTRANCE of Nebby's shop (DO NOT ENTER HER ACTUAL SHOP) and the Hallway with Chara's room. It's a very low chance of happening, but you will eventually be teleported to the area below.
(Yep I copy from Phaltar :) so you should find his/her comment somewhere, and please don't "bonk" me)