I wanted to look into this because that was my initial thought as well. I took the Corruption Perceptions Index [1] mentioned in the article and plotted it against the World Bank GDP per capital [2] for about 167 countries that had data in both sets. Indeed, about 60% of GDP can be explained by corruption level measured by CPI.

[1] https://www.transparency.org/cpi/2021

[2] https://data.worldbank.org/indicator/NY.GDP.PCAP.CD?most_rec...