They’re just taking an educated guess. Based on fossil records we’ve estimated that homo sapiens sapiens emerged about 200k-300k years ago. I’m not sure if they assumed a middle ground estimate of 250k years here, but it was probably something like that. If we’re measuring by years, the margin of error is huge, but when we’re estimating the total number of people, it doesn’t matter that much, because there were so few of us for so long.
They’re just taking an educated guess. Based on fossil records we’ve estimated that homo sapiens sapiens emerged about 200k-300k years ago. I’m not sure if they assumed a middle ground estimate of 250k years here, but it was probably something like that. If we’re measuring by years, the margin of error is huge, but when we’re estimating the total number of people, it doesn’t matter that much, because there were so few of us for so long.