jmcrae,
I’m trying to understand what you mean here. Just saying that St. Paul had reason to become upset if St. Peter taught infallibly doesn’t make any sense to me. Did you mean something like “St. Paul had reason to become upset if St. Peter exercised infallibly needlessly”? (Like how Cardinal Newman was upset that Vatican I issue a dogmatic/infallible declaration that he considered to be unnecessary and unwise.)
No. I have not expressed myself very clearly.
The steps are these:
St. Peter had a vision in which God showed him that all foods are clean.
This was followed by his meeting with Cornelius, where he had the experience of seeing certain Gentiles, including Cornelius, being filled with the Holy Spirit and manifesting healings, tongues, etc.
St. Peter immediately understands the meaning of the vision that God had given to him, so he calls for the Gentiles to be baptized.
Upon hearing that Gentiles are being baptized, the rest of the Apostles call for the Gentiles to take up the kosher law and to be circumcised. The Gentiles refuse to do this.
St. Peter calls a Council in Jerusalem, where the matter is discussed at length. St. Peter, at the end of this meeting, makes an infallible decree - one that is not based in any existing tradition up to that moment in time, and is certainly not found anywhere in the Scriptures available to them (keeping in mind that at this point, not one word of the New Testament has yet been written down) - rather, he is drawing on the oral teachings of Christ, which are not altogether clear (we notice that the Evangelist has to explain to us, when Jesus makes that enigmatic statement about what goes into the mouth and what comes out of the mouth - he explains to us, “Here we see that Jesus made all foods clean,” - this did not become clear to the Apostles until, in fact, the Council at Jerusalem (and perhaps not even then - perhaps it was even later than that, that they finally made the connection).
St. Peter at this point makes an infallible decree that is based on absolutely nothing except his own authority, that the Gentiles will not be required to be circumcised, that they are to hear the Liturgy of the Word in the synagogues, and that they can eat or drink whatever they want as long as they don’t consume blood. Furthermore, that it is permitted for the Jews to partake of suppers with the Gentiles and to eat whatever they eat. This decree is promulgated by letter to all of the churches.
At some point along the way, St. Peter, for fear of certain Jews, sets himself apart from the Gentiles, rather than (as he himself had decreed) sitting down to supper with them and eating whatever they eat.
St. Paul (who as you recall was a Pharisee, and a real stickler for following God’s rules), instead of saying “Whew, he has finally come to his senses and is going by what the Bible tells us to do,” he gets angry with St. Peter and rebukes him for breaking - HUH? - God’s law. Wha … ?
Okay, so how did eating with the Gentiles go from being
against God’s law, to being what the godly are supposed to do?
By the very decree of St. Peter. “What you bind on earth is bound in Heaven. What you loose on earth is loosed in Heaven.” That’s what Jesus said to Peter, in the hearing of all of the other Apostles.
At the Council of Jerusalem, Peter loosed the restriction on eating with Gentiles, and so God loosed the restriction in Heaven. This disciplinary rule was
changed.
How?
By the infallible decree of St. Peter, which was promulgated by letter to the whole Church on earth.
(And then, because he is Simon, as well as Peter, he promptly broke the law, and got rebuked by the Pharisee for breaking it, because the Pharisee knew, didn’t he, how God makes His will known on the earth - it is by means of the Petrine office.

)