What does castellano que bueno baila usted mean?

It's a term used in a song originated by the Afro-Cuban singer Benny More back in the 1940's when big band and cha cha music was big. The song has been sung in the Salsa style that evolved from those times. It refers to the "Spaniard" and in particular the "Castilian" on how well you can dance. The reference had a double meaning back in those days when there was segregation etc.