Not to diminish Cosmo's skills or his excellent explanations, but the tricks used in these speed runs were discovered and improved upon over many years by many different members of the speed running community who all deserve some credit. [1] has a list of techniques and usually notes who originally discovered them. There are some speed runners who are very good at discovering these kinds of techniques but they are not always the ones who are the fastest at running the game.
While the exploit itself was very impressive, I was also very impressed by how clearly he explained it, and how he was able to do it without stumbling, and generally was able to keep playing while explaining. Great communication skills.
1: http://zeldaspeedruns.com/oot/