Funny that a man speaking Herbrew or Aramaic would suddenly throw in a Greek word. As Arsenio would say, "Hmmmmmmmmmm!!!???"
IMHO, the church was built upon the foundation of Christ, not Peter.
Then as now, many people in the region are multilingual. Greek was the culture of the region from Alexander until the Romans, and Greek was the common language, the language of diplomacy, the common language, the coine. Okey-dokey. The Galilee was not particularly Hebrew, and that is where Jesus did most of his teaching when he wasn't going up to Jerusalem undercover. Paul was able to travel widely and speak easily [or shyly according to himself] everywhere, and he ministered to many churches that were not Hebrew at all.
Funny how Arsenio is a Greek word? Hmmmmm??
By the way Campion, Jesus did spend his young life in Egypt and in Egypt of that time if you wanted to make a living as a carpenter you spoke Greek. Even the Jews of Alexandria no longer could speak Hebrew, they had become so assimilated. The miracle of the Septuagent translations from Hebrew to Greek is recalled. In addition Jesus lived near Greek settlements in Judea and many Synogogues of this time had Greek and Hebrew inscriptions.
Jesus very certainly spoke enough Greek to say petros (as Peter is called in Greek). Even the Orthodox Greek Christian Church (which is the nearest to the Apostolic tradition) and no lover of the Vatican accepts Jesus said this to Peter.
By the way, if St. Paul was the one that spread the faith to the gentiles what did Peter do? Peter backed Paul and allowed him to do so. But that is just my guess.