Would be worth asking how it came to be his valley, because I'm inclined to guess it's no coincidence we were dumped here. I would, but Fionn's on a different subject right now. Also, not a bad idea to check to see if he's mentioned anything he shouldn't know.
I'm basically treating his statements the way I'd read statements to old-Celtic style faeries with the whole "cannot tell a lie" thing - anything said directly shall be assumed to be true to his knowledge, anything less than a direct statement could be false. Deceitful, yet honest and true to his word. We can certainly tell that he's very powerful, as well.
And I can't help but feel that there'd be a catch to the whole "take the truck in", thing.