"But to turn your top half to a different angle to your bottom half by twisting your spine is not neccessary. "
To twist your spine to some degree by turning your hips and shoulders to somewhat different angles, actually will ultimately prove necessary in a variety of situtaions if one's dancing is going to advance beyond a beginner stage.
At what point a teacher chooses to introduce the concept, and what words they use to explain it will vary, but ultimately it is a necessary feature of fully skilled dancing. Some teachers may not even think of this for what it is, viewing the situation in a different light instead, but it's still present in their dancing.
Obstinately denying this simply proves the limitation of your education as a dancer.
In terms of physiology, no one with a shred of knowledge of the human skeleton would deny that it is constructed in a way that makes reasonable twist of the spine a motion readily available to us.