It seems as if Stepanich was an adherent of the v2 anti-popes when the article was written. That would make him a heretic if he was conscious of what he was doing and only he can say that. Is he still of that mind?
That in itself would not make him a heretic, but a schismatic. And please do remember that Pius XII had no authority to excommunicate anyone from the Catholic Church, since he schismatically followed antipope Benedict XV, and was a public heretic, who taught baptism of desire and birth control in his Oct 1951 Allocution to Italian Midwives, and thus was not a Catholic nor was he ever a pope.
IMO Pius XIII(II) and Pius XII(I) did not follow the antipope Ben 15 but they succeeded the true Pope( Pius XI-- Card Raphael).
This will be known someday. The very 'election' of Della Chiesa is a fraud and it only follows that he would close the Sodalatium Pianum and condemn the La Sallette Prophesy.
Mc Nutt also hints that he was part of a plot to put the phony coryphee Mussolini into power and that Francis wanted nothing to do with it. ( Mussolini had a long careesr as a Radical Left Socialist and some saw the trick when he suddenly shape shifted into a right wing idealogue.
Ben 15 was also the first 'pope' to suggest publically that the Holy See would not necessarily have a problem with Judaics occupying the Holy Land. Yes he backtracked later but the fact is he was the first. Source-- Vatican and Zionism by Minerbi(J).