Can someone explain my figures please

It maybe is, that nobody really knows, why.

It also could be, your insulin response to the meal and exercise.
Even though you are doing low carb, your background insulin and insulin response will have dropped you a little bit.
There is something called an insulin index that shows how your insulin increases depending on what foods that you have. Chicken is especially high.
Also, it could have been a rogue reading. But only a small one, as being in the 4s is not particularly low. I am non diabetic, my fasting levels are always in the fours, five and sometimes in the high threes. Normal readings are between, high threes and six mmols.
As always it could be anything, it is so individual.
If I was T2, I would be really happy getting results in normal levels!
Control over time is more important than a singular reading.

Best wishes