[EVERYTHING] So why does Bran keep on being spotted?

Granted it was only the second time (the first one was the one when he was grabbed by the Night King), but still, how come the Night King can spot Bran? Or did I misunderstand the raven scene and Bran just flipped out when the Night King turned his head?

Did I miss an important part of the story or is there some magic that is yet to be discovered or talked about which can explain this phenomenon?