Those numbers are in units of "Consumption per Real Dollar of GDP", which is defined as follows: "Calculated as energy consumption divided by U.S. gross domestic product in chained (2017) dollars".
I don't know exactly what it meant by "chained", although from the context it does sound as though it might mean something like "inflation adjusted".
> I don't know exactly what it meant by "chained"
It does mean they tried to eliminate inflation as a factor. In my experience though the basket of goods used for inflation calculations do a poor job representing the majority of consumers' and businesses' costs.
I am getting more and more peeved by using GDP as a single number. Cost of existing, aka housing and healthy food, skyrocketed compared to median income. But hey, the tech got cheaper.