Tszyu was tailor made for Ricky right at the stage that it happened at.
Tszyus mind was set as to how the fight would go already, as he wanted a tough fight for the fans, no pretty boxing match.
Head to head the toughest man won that event and thats how good a fighter Ricky was.

Boxer? Thats another question.

If Floyd or Pac had fought a stand in front of him style of fight they could of made a mistake too, but when you make angles and force someone like Ricky to turn into you you can catch them harder and cleaner over a distance the frustration builds which depletes even more of the boxing skill.