No, it's not about
digestion. I think it's compared to the 'normal' time that non-diabetics can metabolize food/drink. It's basically comparing how our results are in relation to a non-diabetic's.
I think digestion actually begins in the mouth when the saliva mixes with the food (if I remember my high school science class correctly). Some food affects our blood sugar way more than others. Anything made with flour or sugar (or honey, maple syrup...), rice, grains like corn, potatoes, beans will make our blood sugar rise fast and high, but something like a piece of steak or chicken or fish will not. So, these guidelines that we're given by the doctors are really telling us what level we should be at and what level we shouldn't
be at. All this is compared to people who don't have diabetes.
But it's not that simple. Having the elevated reading you had before would mean you don't metabolize the carbs in food and drink as a non-diabetic would. A non-diabetic's blood sugar would rarely spike that high.
Another thing that doctors look at is how long it takes for our blood sugar to come back down to normal after eating. The longer it takes, the more problems the doctor sees for our blood sugar "recovery".
Your 115 after eating the peanut butter on bread and having tea with honey shows that you didn't spike very high as you did before. Peanut butter (the natural kind, not the kind with added sugar) is great to eat and snack on. And of course the bread is a carb but some factors may determine how many carbs are in that bread: how big the slice is, the ingredients of the bread, how many slices you eat. Honey is pure sugar.
I think being aware of this is good but not obsessive. If it makes you eat more vegetables, then this is a good thing! Colorful vegetables like different bell peppers, leafy greens, mushrooms, broccoli, asparagus, cauliflower, eggplant, zucchini, radishes, green beans are all nutritious and filling and better for our blood sugar than potatoes.