Well, it wasn't close to that. The photo below was taken near the middle of the third quarter of a competitive game, and it shows a lot of empty seats. (I got a free ticket, thanks to a StubHub promotion.)
Keep in mind that even when the arena "sells out," the actual gate count is usually at least 10% off, and Wednesday was probably worse, given the cold weather. According to a report from Empire State Development, "Actual attendance during the 2012-2013 season (including Playoffs) averaged approximately 14,974."
On Friday night, the official number was also goosed. The Brooklyn Game reported:
But for a Friday night matchup against the Philadelphia 76ers, one of the league’s worst teams, even the upper decks were half-full at best as the game kicked off. (For what it’s worth, the Nets officially listed the attendance at 16,172, which makes sense if you include the fans watching at nearby bars.)I don't remember whether the upper deck photo below was taken during a break in the action Wednesday--when there would have been more empty seats-- but I was mainly trying to get a shot of the Jay-Z banner, since that's as much of a prideful part of the Barclays Center history as anything.