They're not self-sufficient in energy. They're self sufficient in electricity generation, perhaps, but energy? All the really energy intensive processes that support their way of life - agriculture, manufacturing of goods - those are happening elsewhere. You can't simply equate household electricity usage with the average human's energy footprint, because the two are massively different.
There's a tendency in the west to ignore the painful truth which is that our actions and consumption has far reaching consequences. Everything you buy has an energy footprint, and for many things it's one that we outsource to China. It's great to say "UK carbon output down x%", but if it's because we moved manufacturing offshore, did we really make a difference? It's easy to blame China for emissions while pointing at our renewables as evidence of how good we are, but the reality is that those emissions are often made to service our needs.