To be fair that happens for a lot of different kinds of events, they likely sold all of the tickets they actually made available. They probably didn't open up all of the seats for sale because they knew they wouldn't sell them all so it's better to just block off those areas and set up the cameras so they never show them. A lot of events do that and call it a sellout because technically they sold all of the seats the put up for sale.
Looking online they sold just over 2k out of just over 3k tickets made available.