There isn't much to gain by saying the story is made up along the way, compared to saying it's a grand story from the get go. I could understand him claiming it's a grand story from the start and making people think he's a genius. But the only way I could think saying it's made up as he goes, is to downplay any issues with the story should it not be any good. But I wouldn't think that's the best way to explain the story imho.
I could certainly see him getting closer to his characters over the years, and gives them a better story arc that just love interests for the MC. That's why he's writing better stories for them, that just aren't based on sex scenes.
