Cartesian dualism is one of the many false philosophies that is ubiquitous in our society. It is in practice (and that is the sense I’m addressing here) a tendency to focus on what must be going on in the privacy of others’ minds, rather than their actual words and deeds.
When interpreting the current Pope’s magisterium (or anything, but especially Francis), it’s important to avoid this. As head of the Church, the Pope has the right to be interpreted in accordance with Catholic tradition (and does not have the right to be interpreted otherwise). Interpreting the Pope to be espousing whatever heresies you imagine he must be adhering to, but which he has not actually expressed in his magisterial teachings (or at all) is spiritually dangerous and can lead to intentional disobedience to the magisterium.