they mean absolute numbers
>I tried to compute an estimate of the current percentage of the US population that's forced labor vs. at the peak of the pre-abolition slave trade, and from what I can tell, it's currently higher than it ever was back then.
It's explicitly talking about "percentage" at the start. It would be weird if they silently switched to absolute numbers afterwards.
Whether false by percentage or not, I'm not sure relative percentages are of that much importance. Surely the hundreds of thousands of american soliders dying in the US civil war wouldnt be relieved to hear that perhaps more black people were enslaved today, only to feel their sacrifce justified when hearing it was a mere 0.5%