Fructose has a marked effect on BG. Eat anything with fructose to see the result. If fructose didn't, we'd all be using that instead of artificial sweeteners.
The difference of the effects of 1 gram of glucose is due to an individual's size/weight. I'm small. One gram of glucose raises me consistently 10 pts. I know this from correcting lows. Dextrose works more quickly, but I hate the taste of dextrose tablets.
From eating low carb for almost three years, my body has become quite efficient at converting protein to glucose. I imagine I'm not unique in this regard. I bolus for carbs & also bolus for protein. It seems to be a little known fact among healthcare professionals that protein converts to glucose, but diabetics know from experience that high protein meals effect BG.
Various biochemical processes also contribute glucose to blood, such as cells dying.
I don't see these numbers as random. Complex, yes, but not random. Based on individual biochemistry, effects differ. The only way I've found is to record food & their results to understand what's going on. There is no perfect formula, just trial & error & limiting the variables that we can.