The expression on Trump's face, his body language, his voice, everything about him was a HUGE "tell".
The guy's been badmouthing Obama for five years, never met him, then walks in and, I dunno what Obama said, or did, but you could see by Trump's face, in forty foot high letters, just how impressed he was. Suddenly "reality tee vee" was busted to smithereens by REALITY.
Obama is a true badass.