He used his friggin phone to make the screenshot. That just shows how intuitive he is. And I may joke about it, but it probably is the easiest way to do this when you're not logged into twitter on the laptop.

And <Cmd Shift 4> <Space> lets you take a screenshot of a window!

But at least MacOS screenshot keys automatically save the screenshot. Took me ages to figure out that on XP you have to paste into Paint or something after hitting the 'printscr' button.