At the time of the construction of the temple, various cultures had better
approximations for pi than 3. However, these were used for astrological
calculations. It's probably theologically good that the author wasn't
better informed about current astrology. Besides, he wasn't trying to
teach Geometry 101.
Although one sees rumors that some state tried to legislate pi=3 based on
this passage, the only actual legislation I know of was based on the claims
of a crackpot that pi=4. It passed the committee but happened to be
noticed by a mathematician who succeeded in talking the legislature out of
it.