He even had John Carmack's help, getting a few hints on exactly how the file format worked and how to get it together. Understandably, Carmack also asked him not to post the art files on a public web server, so while the source code is available for developers, the demo isn't actually live for players to try out.
Jones has a much longer post about the actual tech behind the demo, though it may cross your eyes if you're not that code-inclined. It's still amazing, though, and it shows that iOS might actually work well as a portal to development on other platforms. As Jones says, mobile devices often represent a crunch on available resources and performance, and that aligns perfectly with the limitations that lots of web developers are facing as games on that platform get more and more complicated.