The ITF has standard sets of ho sin sul for white-green belts, red belts, cho dans, e dans, sam dans, etc...90% of which, at minimum, are variations on a particular technique, so that a student learns various ways of applying the same principle, instead of learning only a few isolated cases which the student doesn't know how to apply and adapt to different situations. I'm not exactly certain as to the origin of our ho sin sul, but they're pretty straightforward...they might have their origins in hapkido, or really in any other eastern grappling art. I mean, since originally martial arts had a much greater focus on grappling (useful in battle to defend yourself and finish your opponent), a lot of these are the "hidden moves" behind a lot of the moves in our hyung.
I'm personally not worried about the "whence." What counts is that they work, and that I learn them well enough to use them properly.