User blog comment:Neowitch/668 - Pet Axolotl/@comment-3119203-20120523162512/@comment-3563898-20120523171208

Luffy didn't just learn haki in the 2 years. He got much faster and learned some very cool attacks like elephant gun and red hawk, which he wouldn't have been able to do 2 years ago regardless if he knew haki back then. Also, this just shows that Zoro and Sanji know B. Haki. It doesn't state that they know the others which would put Luffy at a great advantage.