As a type 1, I would not be concerned at all with a BG of 7.9.
Someone without diabetes testing their BG soon after eating a carb-heavy meal such as pizza could easily experience a BG as high as 9.0.
I am not aware of a situation where you should be concerned ... but I am not a doctor
We need a lot more information before we can help you. Some background information. What type of diabetic are you, what medications are you on, how long after the meal did you test, what did you eat, did you also test before the meal???