I can't tell whether you were there or not, but I can assure you that when I was growing up in Communist Poland, lessons in the Roman Catholic catechism, taught by Roman Catholic priests, were compulsory in the Communist government schools. Regular attendance at Mass was compulsory in the People's Army. And so on - there was hardly any place in the world where the Church was more Established than in "People's Poland."
PAX was not organized by the Polish Communist Party, but by the Soviet NKVD/KGB. At the close of WWII, Piasecki, a long-term admirer of Franco (his pre-war organization was called the "Falanga") convinced the NKVD representatives in Poland that Poland would be most readily governed through a close copy of Franco's Roman Catholic totalitarianism. PAX was set up by Piasecki on the model of Opus Dei, under NKVD control. Korbonski (who was then the Homeland representative of the Free Polish government-in-exile in London) writes in his history of this period, that "Piasecki became the Soviets' most trusted tool in Poland." The Communist leaders of the government and the party came and went over the years, but Piasecki (on behalf of NKVD/KGB) stayed in control of Poland from 1944 through the 1970s.
The Church's relationship to the party and the government on the one hand, and to KOR and Solidarity on the other, was always flexible and complex. Once it became evident that Solidarity had some chance of success, the Church first hedged its bets and then turned around. And, as in the case of other fallen dictatorships, the Church eventually re-wrote the textbooks to give itself credit for their fall.