Actually I believe that the amount of heavy elements in that star was lower than expected. They used the ratio of heavy elements (uranium and thorium) to date the star, not the quantity. This star, I believe, is what is called a Population II (low metallicity) star. Older stars have lower amounts of heavy elements, and the yet-to-be-observed Population III stars are posited to have no heavy elements whatsoever.

http://en.wikipedia.org/wiki/Metallicity