I don’t think anyone buys that St. Bernard is a “Church Father”. Why not St. Thomas Aquinas then? Pius XII wrote lots of things. One of the definitions of a Father is being a secondary witness to Revelation due to proximity in time with the Apostles. If you’re just a couple generations removed from the Apostles then you can be sure to have some information about what Our Lord taught the Apostles that isn’t recorded in Scripture. St. Bernard was famously asked about BoD and responded basically that, whether right or wrong, he would go with Augustine. He had no independent pipeline, as it were, to Apostolic teaching.
Everything written about St. Bernard in that article could just as easily be applied to St. Thomas Aquinas. Calling him a Church Father is just pious (or Pius) hyperbole.