The TV series is currently set between Eps III and IV. There’s a possibility that it’s about young Boba Fett, though apparently Joel Edgerton, who played young Uncle Owen Lars, is in talks to be in it, and Rick McCallum is saying that it may include a young Luke growing up, which doesn’t sound too exciting really.
Anyway, to the OP, I don’t believe he should be taken literally when he says it was a myth. Many of his off-the-cuff responses have been taken as gospel, and others as lies, when really they’re somewhere in between, a turn of phrase even.
The most definitive explanation that I’ve heard quoted (and I think it was in the Star Wars Insider official fanclub magazine where I read it) is that he never had a story for the last trilogy, but after Star Wars was a hit he admitted to the Press that he did have a trilogy in mind, and also some notes on a story that covered the origins of Darth Vader and Obi Wan Kenobi which he hoped to make one day as a further trilogy. And sure, maybe he could come up with something for a third trilogy. Nine episodes is a good round number.
I think he regretted saying that very quickly, and after Empire Strikes Back was released, he basically recanted the idea unofficially, and then after Return of the Jedi, much more officially because he felt the redemption of Vader was the end of his tale and there was nothing more he wanted to tell.