well I don't know for sure, but that theory is new to me...

black/white dualism has been around for a long time, and applying it to magic doesn't exactly require a stretch of the imagination. I haven't made any serious investigations into the etymology tho.

Crowley used the term in the sense of 'devious', 'corrupt', or 'sinister' magick.

(Which wasn't at all the case; Spare had simply ridiculed Crowley - and possibly rejected his sexual advances - and 'black magician' was the best retort Crowley could come up with at the time.)