User blog comment:Leviathan 89/Luffy real words/@comment-3563898-20110505185713

Maybe Shanks knows about the "Will of D." and that's why he took such an interest in Luffy. Heck, he was on Roger's ship so he must have some knowledge of it. Maybe he also knew about Luffy's bloodline, since he fought against Garp so he knew Luffy could be something special.