First of all, that statistic is not about household emissions, but emissions in total (production only perhaps). On the other hand, it doesn't include all types of household emissions either, because it doesn't account for the entire life cycle of emissions tied to products that has been produced in other countries, and which US citizens consume to a much higher degree than the global average. Household consumption is the main driver of emissions, and high-consuming societies bears much of the blame for the emissions generated by production which has been outsourced to other countries.