The key to answering your question, I think, is to note the intensity of Johnny Dorsett's imagination. For Dorsett, these games extend far beyond typical childhood pretending. When he is pretending to be Red Chief, he speaks about scalping his captives, and later, one of the two kidnappers wakes up to find the child standing over him, knife in hand, attempting to actually scalp him. Johnny Dorsett shows, to say the least, remarkable dedication to his pretend life, well beyond a reasonable limit.
In addition, I'd add that Johnny Dorsett is actually in a very precarious position: he's been kidnapped, and is being held for ransom by two criminals, and yet he treats the entire encounter as a game (and proceeds to terrorize these two criminals in the process). That's not what I'd consider a normal reaction—there's a kind of fearlessness here, to the point that he doesn't seem to even recognize the danger of his situation because he's so caught up in the games he wants to play.