User blog comment:Crow.D.Zoro/Looking for answers/@comment-4031413-20110530164146/@comment-80.217.68.75-20110530204536

http://onepiece.wikia.com/wiki/Canon#Non-Canon

Like Yountoryuu said it was a non-canon episode, we may never really get to know how Luffy found out about Roger and Ace in the manga but that doesn't matter.