It sounds like you may not be aware that the NBA has been actively and specifically blocking criticism of China. It sounds like currently they've reversed that policy on at least what custom jerseys they'll print, but only after a lot of pressure. The NBA is not neutrally "permitting" their players to protest things if they happen to want to, they have taken an extremely active role in what political actions are and are not allowed, and anti-China protests have consistently been on the "not allowed" side, by the league. The NBA, as an organization, is not a neutral; they have chosen sides.
I am well aware of the NBA's actions. The specific question was about an NBA player, which would be the NBA Players Association, not the league itself. They work for the league, in the same way many of the companies HN Readers work for do business in China.