You're right Jin, it does make sense that you could type fast with Colemak. But that's intuition and not yet a fact. The fact is that there are a few really fast Colemak typists and a lot of really fast QWERTY typists and it's impossible to determine at this point what works best judging by speed alone! Of course the fastest ones are QWERTY typists at the moment because they are so many and have so much training. Later on, who knows?
Fast QWERTY typists and fast Colemak typists alike have techniques for fast typing, drilling common words and using some nonstandard fingering for instance. It turns out that when a fast QWERTY typist makes the switch to Colemak he or she will quickly build up speed with Colemak as well but it's hard to determine beforehand what the end result will be and how fast it will develop. Keep in mind that most really fast typists have trained QWERTY from childhood!