Minimum wage in Poland is ~600 Euro / month since 2020, it used to be half that at ~300 Euro.
So that $400 is slightly above the minimum wage back then and the 2018 salary is slightly above the current minimum wage.
The average wage in Poland is ~1100 Euro.
By contrast the Dutch minimum wage currently stands at ~1.600 Euro.
By industry standards CDPR pays quite poorly, by Polish standards they probably pay quite well and there's additional benefits in working for a tech company.
I don't think people who live in western Europe/US appreciate how in Eastern Europe people consider having a desk or office job a luxury by itself as opposed to working in a factory or construction.
They accept lower pay for better working conditions and health. Up until recently Poland was a very poor country and by European standards still is.
You're just not getting the 2k - 6k salaries there that are common in the industry working in Poland.