Hill had short arms, and a longbow like he used has a smaller handle than most modern bows, which also shortens draw. He was also quoted as saying he wasn't good enough to shoot a recurve, which was probably a joke that got legs.
He shot a heavy bow, but POC shafts were probably the only thing available then for arrows, which are hard to get in higher spines. It's logical to think he shot the shortest arrow possible to maximize the dynamic spine.
However, I don't think that 'proper form' will shorten your draw, unless you've been doing it wrong. We are all made differently, and what worked for Hill, or me, or you, may not work for someone else. If you can draw at least to your mouth and get your eye over the shaft while keeping the arrow, your string hand, and your forearm aligned comfortably with your personal geometry, you should be able to achieve accuracy with carefully matched equipment. Draw length is secondary to that.