Paul calls Peter's staying away from the Gentiles "this hypocricy" because Peter was pretending to be like those Jews who say that Gentile Christians have to be circumcised.
Here to be "led astray" is a metaphor for being persuaded to do something wrong. Alternate translation: "Even Barnabas was persuaded to be a hypocrite because of them" (See [[rc://en/ta/man/translate/figs-metaphor]])