They didn't get access to the actual NASA software running in space. They wrote simple example programs to exercise the CPU emulator. The example program that is loaded when you first visit the web page simply counts down from 10.

And having the actual NASA source code would not be very useful, since the actual software interacts with complex hardware on the spacecraft, which you would have to emulate in addition to just the CPU. For example, the FDS computer interacts with all of the scientific instruments, the digital tape recorder, the telemetry output hardware, and the other two computer types on the spacecraft. (I'm not casting shade on the CPU emulator as it is an impressive achievement and the code is very high quality.)

It's not my project but presumably someone has a copy.