How does he argue that? Bp. Fellay is not a Dominican.
Fr. Albert, O.P. thinks that the SSPX(and it's superior general) is a higher authority than the superior of the Avrille Dominicans, to which Fr. professed his vows. Fr. tries to argue that since +ABL helped them get established, he and his successors would be the true superiors of the congregation. The Archbishop explicitly said he was not the superior of the Avrille Dominicans and placed his trust in the prior.
+de Galarreta is also not a Dominican, merely complicit in this "illegal" foundation. The neo-SSPX saw that Avrille was not going to go along with a deal with Modernist Rome and had to establish their own group of Dominicans who would not speak up.