I believe his point was that people arguing the NFL passing a policy that prevents kneeling is a violation of freedom of speech is wrong.
If the government passed a law that says NFL players must stand for the National Anthem, yes, that would violate their right to free speech as stated by the First Amendment. But, if the NFL teams, as private employers do so, that's within their rights as employers.Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.