B dances in a manner that he manages to seem present/involved and at the same time distance/detached.
gets attention as if by seeking to deflect attention (it).
B dances in a manner - what sort of manner
with an undemonstrative panache - strange expression, undemonstrative suggests not flamboyant, while panache suggests flamboyant.
So he dances with a style that seems to draw ones attention = gets noticed
How?
as if by seeking deflect attention by understatement,
yet
he manages to seem involved & yet aloof.
gets attention as if by seeking to deflect attention (it).
Not sure which part is giving you trouble.
Hope this helps.
See what others say.