Well, it's plausible seeing as how multiple people have reported to be able to play the game while lacking internet connections for up to 20 minutes. Additionally, the methodology of the code seems to fit with several of the changes made by Maxis to improve performance (disabling cheetah speed for example).
The main thing the article proves is that the servers aren't needed for any real time calculations. What's to say the servers don't provide valuable data based on previous events in the game, data that's needed for future simulation?
Regardless, Maxis has stated they will respond shortly to the article. https://twitter.com/rockpapershot/status/311618456640450561