There have been 85 confirmed NBA players with Covid, including 48 based on the testing through the end of November. The CDC has reported that 40% of those with Covid-19 are asymptomatic. This percentage is actual higher than the national average, likely due to increased testing by the NBA of all players on a regular basis.
Even if we conservatively assume another 85 had it and didn't report or were asymptomatic, that would not even be close to "Most".
And since all players are tested regularly for purposes of attending practice facilities, etc., and the league, being worried about false positives, has been concurrently doing antibody testing since July, having 85 undiagnosed cases is very unlikely. Because of the robust testing for the virus and antibodies, the undiagnosed number is likely closer to 0 than 85. That would mean over 2/3 of the players have not had Covid.