Stores, and to a lesser extent magazines and major game sites, will often make educated guesses about when things will be released. The games media is often pretty good at this, although even they make plenty of mistakes. Stores seem to dislike having a TBA so they're more likely to make up a date, and there seems to be some rivalry where they all want the earliest date, as if someone would order from a store because they say it will be out sooner.
Sometimes even products are made up. For several
years various stores and gaming magazines would list an upcoming PS2 game called "The Elder Scrolls Adventures." Bethesda denied this several times, and on occasion the products didn't even make sense - once Amazon suggested that The Elder Scrolls Adventures was a stand alone TES III Bloodmoon.
The rumor appears to have started when Bethesda mentioned having a completed design document for The Elder Scrolls Adventures II: Eye of Argonia, the sequel to Redguard. They also said that they didn't have any plans to develop this at the moment but might consider it for consoles as those audiances were more receptive to this style of game. Someone apparently decided this was sufficient to put the game in their upcoming game release pipeline and it was ages before the rumor was finally put to rest.