maybe to you, but certainly not to a lot of 19 year old guys, and the idea that there is no other way to interpret it is problematic.
sometimes I think understanding these seemingly insignificant misunderstandings could help shed light on the much more harmful and dangerous ones that happen too often between men and women.
edit: to be clear, he didn't misinterpret it as guaranteed sex, but interpreted it correctly as a (momentary) sign of interest, and by asking her out acted completely according to accepted social norms, but was then basically led to believe he'd done something slightly inappropriate. Believe me, I'm not nitpicking here for the sake of it, but because I think this may be an interesting test case for other interactions.
There is only one right interpretation in these situations the others interpretations are pointless to discuss.
I think you should be having those discussion not with the person you went out with but with friends that are better at dating then you are. I mean the post that we are specifically talking about, the dude sounds like he lost his cool a bit at the end.
If any one want dating advice I and I'm sure a few others in the thread are more then willing to dispense some in PMs or whatever.