ok i correct myself i watched that video again and yes some of those kicks looked like TKD. but that's 8 knockouts in UFC history, and UFC has had about 324 fights, so I'm still not convinced that TKD is a martial art that a lot of UFC fighters use much
You didn't pay much attention, then. Mirko Cro Cops career is described (in that video) as 'one one-kick knockout after another'.
And since the title of the clip is "Ultimate 8 [...]", it's not rocket science to figure out that there are more than eight to choose from.