Rhetorically, it's a distinctionw without much difference. He was speaking metaphorically. He was rather brusquely referencing people who are drawn to, and have always in their mouths, the mud of negative talk. In the context, he was speaking of sinful defamation, aspersions, innuendoes. Similar concept: muck-raking. Conveys the idea of uncleanness in the mouth.
There are those who defend the words and actions of this Pope no matter how outlandish, outrageous, or inappropriate.
That a foul reference to a filthy sexual perversion could ever be considered edifying language for the purpose of “teaching and sanctifying” is extremely sad.