That anybody can get anything done with such constraints is amazing to me, but he's obviously quite good at it.
Cut to a few years later and now I have 3 high resolution screens in front of me, pretty much all the time. I still tend to use just my laptop screen with tmux though, with the rare exception (during deployments, mostly).
I won't say that a single small screen is better, but I do think from personal experience that, after some time and initial effort, it really is not the handicap people think it would be. It certainly won't slow you down like a thumb keyboard will.
Being broke, I ended up with a Toshiba netbook that couldn't handle more than a few browser tabs at once. Installed Debian to squeeze out some performance over Windows XP (first foray into Linux). Best thing that ever happened to me.
Soon I learned vim, tmux, and had my entire dev environment in a Guake terminal overlay that I could quickly toggle in and out of view. It was like having two full screens in one.
My work just bought us monitors and everyone is dual/tri-screening it. I just dock my laptop and use the single monitor, still using the same guake/tmux/vim setup.