apparently you missed the “over time” qualifier in the article. Only about 20,000 standing population.
Apex predators always have a smaller population than their prey or famine and cannibalism are next.
Humans figured out a better way.
I instinctively knew BEFORE reading the article there is just no practical way Billions of T-Rex’s could inhabiting at the same time in North America. Of course over 2 or 3 million years that is quite possible.
If humans survive 2 million more years, what will be the cumulative population over that time? Could be beyond the scope of a 64 bit based computer in integer form.