Why would it even be okay at all for a piece of code that determines the seed for a pseudo RNG via observation of hardware events (a Geiger counter measurement, according to the article) to even access the date and time on a given system? It should have no use for that information, and with a piece of code of that criticality, one would expect auditors to scrutinize any and all syscalls that it performs. This way it should have been fairly obvious that it's requesting the time from the OS, which it shouldn't do in the first place. Mocking date/time info is unnecessary if your code under test is entirely unable to get time information from the system in the first place.

All of the brightest minds were building Facebook ;)

I feel like generating a lot (100k? You can tweak to get whatever confidence you want) of numbers for every day for the next several (30?) years and running tests like chi-squared (or others, see http://www.cse.wustl.edu/~jain/iucee/ftp/k_27trg.pdf) doesn't seem too crazy when you're talking about millions of dollars in prize money.

What if the rigging was only in a certain year? Auditing each day for the next decade would be safer. A good code review sounds even better.

While code review isn't foolproof, this seems like it should have been fairly obvious.

Well, more than is practical to run, probably.