Buakaw didn't have an "alien style", he just managed to adapt and use Muay Thai to great efficiency in Kickboxing using what they do best; teeping, roundhouses and clinching. A big factor to why he was so dominant as well is that compared to his Western and Japanese opponents who all had about 50 fights or less at the time, he was already on about 200 fights.
He might have been using less punches than the others, but he's actually a pretty solid puncher and has a lot of punch KO's, and his defence might seem unorthodox but it's definitely underrated when it comes to blocking and dodging punches.
Around 2007-2008 his style started to be figured out in Kickboxing though and some adapted to counter it. Masato for instance in 2007 was the first who really seemed to have put in place a good strategy to counter Buakaw's style using better boxing, while Sato managed to KO him with punches in 2008. Same with Albert Kraus who outboxed him in 2008, and then there was the Dida scare in 2009 where he nearly got finished with punches too. So his style wasn't unbeatable and those years 2007-2009 were a bit bumpy for him.
However I'm a big fan of his style and he opened up the eyes of many when he first appeared in K-1 Max, especially during his 2004 run for the world title.