Extreme poverty dropped from 44% of the global population in 1981 to just 9% in 2019.

They actually did adjust for inflation.

We study poverty in the now-conventional sense of living on less than $2.15 per day in 2017 PPP dollars (World Bank, 2023), using both consumption- and income-based measures as available.

1 These rates are based on the $2.15 2017 PPP poverty line (Chen and Ravallion, 2010; World Bank, 2023). See https://pip.worldbank.org/

https://vincentarmentano.com/research/hpf/howpovertyfell.pdf (Bottom of 2nd page)