The long-standing perception has been that the complete Star Wars saga is a 9 film cycle, and after Episodes I through III were finished Lucas would move on to Episodes VII, VIII, and IX, resuming where Return of the Jedi had left off. "That's really not part of the plan AT THIS POINT, " he says. "When you see it six parts, you'll understand. It really ends at part six."
When he says he never came up with sequels for the 6 movies as they are now, he's talking about the fact that the story always ended with the Sith being vanquished. Originally, he was planning that resolution to take place in Episode 9, but he decided to cap it all with Episode 6.In 1999 He's talking about sequels to the story he has now, which ends at episode 6.
Back then; he was talking about that same story taking 9 films.