Microsoft promises Milo is the next step.

[NJ5]

Maybe those who believe it's not scripted are not aware that speech synthesis (nevermind speech recognition or AI) is not sufficiently advanced to generate the correct, flowing speech that the demo had.

Asking for proof that it was scripted is like asking for proof that Santa Claus doesn't exist. It isn't really possible to prove it, but common sense and a little knowledge (if you have it) will help you see it.