It’s anyone’s guess really, how far apart were the tests? Sometimes for me I can liver dump if my BG go below 4 my liver compensates and my BG can go up
full fat milk has carbs so depending on how much you had it could have contributed, some people find that sweeteners trigger the same response as sugar, your body thinks it’s getting something sweet so it deals with it the same, BG isn’t linear and there’s more than food that can affect it, the weather, exercise, stress, lack of sleep
How long after eating did you have the coffee? You could still have been on the rise from previous food if it was less than 2 or 3 hrs
I’ve seen some forum members report that even coffee has affected their BG, I’ve never experienced that though
It’s only a rise if just over 1 - allowing for meter accuracy it could have been less or more.
The best way to know if it’s what you drank that affected you is keep a food diary & record everything and test it a couple of times or more to see if there’s a trend