You're asking him to prove a man determined word, so you're going along with writings by human as well by using the word in context. So of course he should as well, and he did.
No I just want him to phycally prove that oxygen exist.
He can't physically prove to you the Earth exists from his current vantage point.
He can post pictures, and you could just say they were doctored.
You're asking him to prove a man made word with a man made definition, but you don't want him to use man's science tools. That's hypocrisy.