This is not visible in English where the (historically) formal "you" is the default, but in languages that have clear separation between familiar and formal ways of addressing someone, people tend to use impersonal forms when it isn't obvious how one would wish to be addressed - if I'm reading the definition correctly this is a form of avoidance speech.
My SO uses it addressing my mother because a few years ago she asked about this and got the response that the formal term is preferred. In the meantime we became parents and it's becoming increasingly awkward.
I don't think personal/formal (tu/vous) forms of addressing count as avoidance speech, and neither does the normal switching between casual and formal registers depending on who is addressed, because so many languages make that distinction, whereas according to the article, avoidance speech is a rare phenomenon. Even Japanese, which has an exceedingly complex system of reflecting social hierarchy in speech, doesn't seem to count has having it.
Rather, the defining feature seems to be that avoidance speech reflects an actual and specific social taboo rather than a simple difference in status.
My SO uses it addressing my mother because a few years ago she asked about this and got the response that the formal term is preferred. In the meantime we became parents and it's becoming increasingly awkward.