I will try my best to explain what I know.
NBATV is a channel. It carries NBA games....NBA classic games....talk shows concerning the NBA, etc.
LP is something you can purchase from the NBA. The league shows games that are being televised by various channels around the country. They purchase the right to show those games on a package called League Pass. They are not channels then, but are simply broadcasts (by the League) of games that are already being shown in various venues around the country.
Clear as mud?