And we still had rich and poor.
Poverty is when you don't have a good place in society, lack of respect by your fellows, and no security for your physical safety or property.
I think this article also does a good job in emphasizing country-level poverty is what's really important to think about. That is, in the US, since we already have the infrastructure of a rich country, even poor people can afford safe food and refrigeration (but even then it's not evenly distributed, e.g. much has been written about "food deserts" in the US).
But, in say, Nigeria, they are so undersupplied with refrigeration trucks that making it possible for the poor to get reliable access to safe food would take a massive investment, which would mean a lot more energy.
In 1800, almost everyone was destitute by current standards, even prosperous merchants. Child mortality rates were appalling. And at the same time, there was a spectrum between relatively rich and poor, and merchants appeared “rich”.
The article is solely about absolute wealth levels, and is making empirical claims about energy requirements to get there. Concerns about wealth inequality are orthogonal to this set of claims. You could have incredibly equal or unequal societies, but none of them can (with current technology) produce low child mortality rates with very-low per capita energy usage.
If you measure wealth by dollars or iPhone access, this tautologically true but it's not a good measure of how life was. A wealthy person had enough food, access to leisure, a large house with luxurious possessions and probably servants. Sure, health care might have been bad and they might have died of various epidemics. Their lives would have been far more appealing than the life of, say, someone working 60 hours per week in a factory (who has some health care but risks on the job injury and is worn down by the stress and routine - even if their cheap Android would have worth a trillion dollar in 1800).
As other have noted, the industrial revolution also got much of it's impetus from peasant being driven off the land they cultivated.
Or to direct the energy differently, e.g. shift some of it from rich users to poor ones.
> in the US … even poor people can afford safe food and refrigeration
Poor people are living homeless in tents and cars. They can not afford safe refrigeration and many do not have good access to safe food.
If you only care about there being a delta between the rich and the poor, sure, there have always been rich and poor people. But that neither usefully describes the world, nor does it account for what poverty actually means and how poverty levels have changed in the last century.
Hans Rosling used to make a joke that the top few percents of students in the Swedish educational system knew less about the world than a chimp (based on the reasoning that if you pick answers to questions randomly, you'll be right more often than the students).
I can recommend watching some of Hans Rosling's talks about poverty and reading his books. It is important to understand what poverty means.
In pre-industrial times, and even modern times, those who were able to compel (or force) people to work for them – i.e. provide them energy – were those considered to have a higher social standing. Those who provided the energy were of lower social standing.
The rich of ancient times had to scrape their wealth from the labour of _so many_ people.
Meanwhile, if we tried applying the ancient poverty line to a modern rich society, we'd have trouble defining it clearly, even homeless people might sit above it, it barely makes sense.