The hypocrisy Paul spoke of was that Peter had been eating with the Gentile believers on a regular basis, but had stopped when the men sent by James arrived in Antioch.
Paul stated earlier in Galatians that Peter was afraid of the Jewish circumcision group sent from James in Jerusalem and the other Jewish believers followed his example. I don't understand this because in Acts 10:11-29 Peter was given a vision or dream from God to teach him that nothing God creates is unclean or impure. He even stated this to Cornelius the Centurion when he arrived at Cornelius' house.
While talking with him, Peter went inside and found a large gathering of people. 28He said to them: “You are well aware that it is against our law for a Jew to associate with or visit a Gentile. But God has shown me that I should not call anyone impure or unclean. 29So when I was sent for, I came without raising any objection. May I ask why you sent for me?”No wonder Paul thought Peter was a hypocrite!