They must have bought prototypes and are selling them. Wouldn't TI announce that they're selling them or a bunch of people be selling them at the same time for it to be legit?
They might not necessarily announce the exact release date at all. When the PRIZM came out, nobody knew until they saw it appear on Ebay.
Also if the site is based in USA (which is most likely the case, seeing the prices) it's most likely using M-D-YYYY format.
Maybe the calc is about to come out and they're just trying to get them delivered early so that on the official release day people can get them immediately?
But yeah it's still kinda weird since this seems to be the only site to have them in stock right now.
EDIT: They're based in Grand Rapids, Michigan, United States.