Cardinal Müller has always held to the orthodox teaching of the Church as set out by St John Paul II in Famliaris Consortio. Pope Francis according to his letter to the Argentine bishops no longer seems to hold to the teaching of Familiaris Consortio and when asked to clarify his position resolutely refuses to do so.
I agree with Cardinal Müller's interpretation but what I can't understand is how he reconciles his interpretation with that of the Pope. I can only think that the sacking by the Pope of three of Müller's staff before Christmas and the Pope's refusal to even tell the Cardinal why he had to sack his priests let alone the priests thenselves has forced Cardinal Müller to make an attempt to appear to be backing the Pope.
When people talk of the Curia they think of the Cardinals. They forget that there are many  much lower ranking clergy working hard there. It is said that these people are working in a climate of fear these days: I wouldn't be surprised.