He actually doesn't. If he is truly attending an indult (if you have a sense of humor, I first typed insult) mass, then he is following the Popes, he believes has authority. He is probably in a better position than you, because he is consistent and doesn't follow his own lead.
The problem I have is that I am not sure the body and blood of Jesus is there in his mass, because all the changes were so drastic and we don't have a current authority we can trust.
Gray you clearly struggle with basic logic. The changes of vatican 2 contradict what the church has always taught. The Vatican 2 claimants were/are public heretics and apostates and promote those errors.
The logic of the changes of the new rites make clear to me that I must avoid them to be consistent with what the Church has taught barring the contractions of Vatican 2.