Who knows? Because he's a smart kid and knows who Tony is and he would be younger, probably the only real successor Tony has. Unless he ever has kids.
Nah man. It's just the kind of hearsay that the general public makes assumptions about when they see source-material derived movies like this nowadays. It's a mentality of filmgoers that started manifesting back during the LOTR releases when people who never read the books started seeing the movies. They'd sit next to someone who read the books, who would fill in the blanks for them. Now that's evolved into comic book flicks, but there are new fans who want to be part of the "informed" so they just say the first nonsense that comes to mind that makes easy sense to them to sort of fill-in the experience.
"Oh.. there's a young kid in this one, so that must be who takes over for Iron Man when he grows up!"
It's the same kind of critical thinking error that the majority of people make about their uninformed stuff every day.
It's pretty simply actually.