But I'm not sure if that applies to foreigners, too.
It does, certainly if he's from within the EU.
I have personally heard of countries like the UK, Slovakia or even Malta
I've personally done translations for the tax office about this. The department that goes after people who do this. They are not known for leniency, especially if VAT is involved too.
Any sort of tax fiddle is dodgy, particulalry now that it's easy to prove if someone is actually residing in Poland and issuing bills as if they were abroad.