I do not think it as as conclusive. Non-diabetics spike over the guidelines as well and may also have foods that spike them longer than average; I believe it is more bout the length of time a spike remains and what the starting reading is.
My wife measures blood glucose of those on her weight loss program, so far no one has a lower blood glucose reading than me, and my wife has not had a lower fasting blood glucose than me on the 2 times we have tested at the same time, she has been in the 5's (but I am stricter low carb and I train more).