What is confusing about the encounter with o’brien?

The incongruity of this initially experience is based around the way that while O'Brien is putting on a show to be an individual from the Brotherhood who starts new individuals into opposing the Party and Big Brother, he is exactly the inverse. He is putting on a show to be what he is not and is, truth be told, some individual who works for the feared Ministry of Love, distinguishing and tormenting individuals like Winston and Julia who might oppose Big Brother and the Party.