In China, the Occam's razor explanation is that the lead is really there. China's population is freaked out by food safety because of all the food scandals that have happened over the years. Melamanine in milk, for which milk company executives were actually executed, reuse and reselling of cooking oil found in gutters, the list goes on and on and on.

I have no idea about the conditions in Taiwan, but in China, the Occam's razor explanation is unfortunately the negative option because it's proven to be so common. Recently for example, Hong Kong folks are super mad that mainland China folks are coming over and buying up all the milk powder for their babies. Why don't mainland China folks buy milk powder in mainland China? Well, there you go.

edit: for those who haven't read the article, the article states, "The researchers found the highest levels of lead in rice from China and Taiwan"