So we learn in Some Like It Hoth that there needs to be a body for Miles to "read" someone. That's why he has to lie about that guy's son. This limit seems to apply everywhere else, as he only hears something when he's near a body.

But here, he isn't anywhere near a body when he "reads" the grandson.

Why is this? Does there just need to be a body somewhere? Or had they just not decided on that particular limitation at this point? Was he faking it? What?

One of the unanswered questions. He also says in SLIH that he can't have conversations with the dead, that's "not how it works." But he's definitely talking with the grandson.