They might be saying that because of 'midnight release' or early access stuff. But the official launch was the 28th.
It depends on what time zone you were in. The game was officially schedule to launch at midnight Central time between April 27 and April 28. If you were in Central or Eastern time, this would have made the launch on April 28; Pacific and Mountain time would have been late at night on April 27. Just before launch, however, they changed the time to 11:00pm Central, which made it April 27 in Pacific, Mountain, and Central; and the stroke of midnight between April 27 and April 28 in Eastern.
News item announcing launchSo given a choice, I'd call it "scheduled" on April 28, but it actually happened on April 27.
Likewise, I consider the "shutdown" date to be December 1, because it actually happened about 3:20am December 1 Eastern, which was 20 minutes after midnight on December 1 Pacific time. Only places west of the mainland U.S. had it shut down on November 30, although that was the "official" shutdown date.
P. S. Although really, I'd consider the game's launch date April 25, since that is when the head start began and the servers were publicly accessible for the first time to people who weren't specifically invited by the devs earlier.