William Langland published The Vision of William, Concerning Piers the Plowman in 1362. The Protestant Reformation was a movement ot the 16th century. Martin Luther, the father of the Reformation, wrote his life changing 95 theses in 1517. It was only after this that Protestant theology came into being and developed along lines in some regards antithetical to what we call Catholic theology.
This shows that at the time of Langland's writing and publication of Piers the Plowman, there was only one Western Christian Church (Eastern Orthodoxy came into being earlier at the Great Schism of 1054) and it was the Church of Rome. It is called Catholic because of its origins as the one "universal" Church of Christianity, which was then called simply "the Holy Church."
What she were witterly that wis'sed me so faire. 1.074
"Holi Chirche I am,' quod she, 'thow oughtest me to knowe. 1.075
I underfeng thee first and the feith taughte.” 1.076
Therefore, it must be said that Piers the Plowman follows the Catholic ideal, ideology, and theology. This is one reason Langland was so popular among the clergy and rising middle class: his didactic (instructive) poem strengthened the population's religious beliefs.