I don't know how they found it, but I'm glad to have discovered it. It was listed under "Special Advance Preview" so maybe the person searched for that for Seattle. It does pop up there for that title if you search it with Seattle.
And this supports the whole 10 original cities + 10 more probability.
ETA: And with that, a "Special Advance Preview" sale for May 26th at 10 pm for Washington D.C pops up. It's exactly the same as Seattle is, except it's a new exciting city. (Though it would be funny if this were something entirely different. It's hard to guess when everything is unlabeled).
ETA AGAIN: ooooh, it seems fandango is listing everything as sold out now. Maybe they realized people were buying things too soon.