Can someone explain this listing to me?

One possible explanation is that it was a shadow inventory unit, or possibly one that was slated as a rental, that a prospective buyer wanted to purchase. Typically developers only release a certain percentage of available units, but if someone says: "I like the layout, but would rather purchase on X floor" they won't say no.

It depends on the seller realtor. If you look at that building itself, there are many other apartments listed for sale. Just because it's in contract doesn't mean it will go through. If you look around different apartments and track them, you will see they go into contract and then become unavailable or re-listed when that deal falls through. When I went into contract with my coop, it was updated by the as "In Contract". A week later, it becomes unavailable (we were in attroney review) and it was re-listed a week later under a different company. It turned out that the selling realtor's firm was bought out and merged with Corcoran so the original listed became unavailable. Look around, you will also see apartments been "In Contract" for a long time before it was sold, typical in these days with the banking/financing process. Good luck.

To echo what Maly said: I had a situation like that once, where I wanted to buy in a particular building but the first deal fell through. Nothing else was listed as available in the building, but the broker had another apartment coming on the market in a few months, after they completed a gut renovation. So I saw it, we agreed on a price, signed the contract, etc. -- without it ever being published or listed anywhere. Then, after we signed the contract it was published in the NY Times and Streeteasy (listed as being in contract). I honestly never figured out why they bothered doing that -- maybe in case we didn't close? Or maybe just to establish a record of offering prices to try to game the market? (It was listed for quite a lot more than we were actually paying...it was a little odd.)