Hard to tell at this resolution, but it looks like he's using a fairly bare X setup with a tiling window manager and only one Emacs frame on the left. The colours and layout on Emacs look like org-mode. Does he write with org-mode? I would have expected him to write bare TeX, of course. Maybe he's doing something else with org-mode.

He's got Xeyes on the right, and the shell windows could conceivably be Emacs too, but if so, he's customised them to remove the minibuffer.