It kinda doesn't matter where you start counting. Exponential curves put almost everything at the end. Adding to the left side doesn't change it much.

You could go back to Lucy and add only a few million. Compared to the billions at this specific instant, it just doesn't make a difference.

I would imagine this is probably the source, which benchmarks using the last 200,000 years. https://www.prb.org/articles/how-many-people-have-ever-lived...

Given that we only hit the first billion people in 1804 and the second billion in 1927 it's not all that shocking.

That argument works both ways, it might be significantly higher depending how you count.

But this is also just the non-intuitiveness of exponential growth which has only now tapering off.