'What's the matter?' asked Charlie, leaning up on his elbow beside the fire.
'Where is the rider?'
'There is no rider that I can see.'
'If the rider appears, you may wake me.' He turned and fell back asleep. (pp. 76-77)
It's perfectly in line with Eli's ability to follow his genuinely kind impulses and then switch instantly to utter disregard when it's pragmatic. It's absurd and funny, but not in a Monty Python kind of way. I expect it mirrors somewhat the split between how people really spoke in the west where the book is set and how the contemporary Eastern writers of Westerns voiced their characters. DeWitt manages it with great skill.
I was a bit taken aback, though, when Charlie, mocking some trappers dressed as parodies of themselves, says, "where do you even get a hat like that?" (p. 148). This seems to be a very modern use of even, one that Mark Liberman has discussed on Language Log. Not that it's a big problem, but it did bring me out of the book and back to my default linguistic preocupations.