As more proof, Paul lets us know that these people “added nothing to me.” Or, stated differently, they found no fault with his Gospel, and therefore did not need to correct him. Moreover, they saw, they recognized, that Paul had “been entrusted with the Gospel for the uncircumcised, just as Peter had been entrusted with the gospel for the circumcised.” And so they all agreed that Paul and Barnabas would go to the Gentiles, and Peter and the others would work on sharing the Gospel with the Jews.
This question by these money changers and livestock peddlers is essentially the same as those who complain about Cancel Culture. Rather than take the public outrage as a correction, and a chance to learn, they push back, attempting to prove their innocence. It’s not my fault; I did nothing wrong; why would someone do this to me; don’t they recognize that they are infringing on my right to live and make money?; I’m the victim here.