Earlier quoted context omitted.
I find it unlikely that even a state actor would have access to literally all the same private data that ProPublica has acquired over the years, and that they'd know what data ProPublica has and what can be safely manipulated.
This is a straw man. There is no reason they would need ‘literally all’ of Propublica’s data. We don’t know how many data points were verified, but it need not be many.
So we know it was at least 50 data points and not all of them were public. It was likely many hundreds of data points since it would be trivial to check more than one number if you already had 2 copies of a tax return pulled up.
If we take ProPublica's words to be accurate, then how would a state actor know exactly which 50 individuals ProPublica would have access to given that they would have a vast network of contacts and can and did ask the individuals involved to review the information they received and point out any inaccuracies.
Either these are real tax returns, ProPublica is lying or the state actor has a crystal ball.