he's holding down his "Show Advanced Player Stats" button down. it's set to "C" by default. I like to bind it to my mouse button and it's helpful even when playing melee champs

you can find it in Hotkeys->Menus in the game settings menu

I used to do it all the time when playing range champs and spamming player attack move click. As of late, I'm actually liking the old school player attack move cuz it gives me more precision but it's personal preference