A lot of ladder is being as fast and efficient as possible with your movement. Build orders, creeping, managing your fights, macro/micro... its actually very similar. Except the AI in the campaign is totally predictable, you can practice the same scenario any # of times to find the best way. Playing a human is always slightly different, things change and you cannot play the same way always.

The best competitve players would blow this guy out of the water if they decided to speedrun. The creativity involved in actually challenign the metagame of multiplayer is way more than what you need to speedrun the campaign. Fooling the AI which never changes versus fooling a human who plays the game just as much as you. Not even close. Plus competitive players have much better micro and macro.