1. While my uncle did marry a divorced woman, that doesn't mean he wasn't validly married. Could be any number of reasons, including: Pauline/Petrine privilege, annulment of her previous marriage, or the previous spouse is now deceased. Terminology can be muddied in the modern world. Yes, sometimes people continue to identify as divorced even though they are not, or a widow, by Catholic thinking.
Look, words have meaning. If your uncle is validly married according to the Church, yet says that she was "formerly divorced" then he is using faulty terminology and those who interpret the use of the word "divorced" as meaning "formerly sacramentally married" would not be wrong.
In the case of the pauline/petrine privilege, the woman is not "divorced" in the eyes of the Church since her first "marriage" was just a natural union and not a true, sacramental marriage.
In the case of an annulment, there was never a marriage, so divorce isn't supposed to be part of the explanation.
If your uncle used correct terminolgy, then the "talking behind his back" wouldn't be bad but just truthful fact-sharing.
Example: If when i was 6 years old, my younger brother died in a car wreck because I didn't buckle his seat belt like my mom told me to, of course this is an accident. But if I walked around telling people "When I was young, I killed my brother" they would rightly interpret that I actually, physically killed him...because those are the words I am using to convey the idea.