Not bad for a culture without telescopes, computers, atomic clocks and other high-tech goodies.
Technology is beside the point. All you have to be able to do is count days and see the moon a few times a month. What's impressive is the attention span, but more than that it's the conception, or apprehension, of the celestial movements.
Note though, that in 12,000 days the 365 day year drifts by about 8 days from the tropical, i.e. seasonal, year. This is a slow drift, and evidently didn't concern them, just as it didn't concern the Egyptians.