It's not against YouTube's ToS to run pre-roll ads of any length, of course. But I think he was just selling get-rich-quick schemes or something. At the time YouTube ads were more rare and generally short, like 15 second TV commercials, so it was weird to see long-form content as ads. He absolutely saturated the site with this ad for a while to the point that it became a meme. I'm guessing a significant percentage of YouTube's user base at the time was served that ad at least once.