Saint Paul never heard of Saint Athanasius, either... but Saint Paul was an Athanasian Trinitarian.
How do I know this? Because "Athanasianism" is just a theological catch-phrase which describes "Believing what the Bible teaches on the subject of the Trinity". And Saint Paul believed what the Bible teaches.
Likewise, "Calvinism" is just a theological catch-phrase which describes "Believing what the Bible teaches on the subject of Predestination".
Calvinism also implies schism. I know of no evidence that St. Paul or St. Augustine would subscribe to such an approach as that.