He did look like thisYou blew his mind when you challenged what he had presented as an unquestionable truth.
You see, he didn't think of his statement as an unsupported or even flawed notion, he likely thought he was enlightening you to what he'd always considered a universally obvious fact - thus his "deer in the headlights" look and inability to even discuss it further with you.
Hopefully, he will further consider the weakness of that notion before blurting it out there again and placing himself in a position to look foolish when it isn't the conversation ender he thought it was.