According to the Cambridge English Dictionary, 'minx' means 'a girl or young woman who knows how to control other people to her advantage'; the Oxford Dictionary appears to have never heard of the word; the Urban Dictionary it means Cheeky or mischievous girl.
As I felt puzzled, I also checked internetslang.com (if there was to be any likely offender, it would be internet usage/slang) and they also say that minx is a cheeky or mischievous girl.
Am I looking in the wrong dictionaries 
Had my son reacted that way regarding a 23 month old little girl, I would have been seriously angry with him that he would think I would use a derogatory term for my own granddaughters - he wouldn't have left without saying goodbye, he'd have left with a flea in his ear for being so rude.
I also wouldn't tolerate him messing with his phone either - completely unacceptable behaviour when visiting, he might just as well say out loud that he'd bored!
You have absolutely nothing to feel bad about Thistledoo - you have used the word the way most of us would use it; you can't be held responsible for people who don't understand word usage.
It’s been a while so I will start us off…….whats for supper and why?


by way of apology - you don't deserve such treatment. 
