A1C is an approximation of the total area under the curve, wether as spikes or high basal bg.You can be insulin sensitive and have a high hba1c as well due to a chronic high carb or high calorie diet, constant glucose spikes can up the average or having prolonged high fasting glucose level weather that be from liver dumping or stress hormones or what have you
I would think logically if you return to baseline fairly quickly that you are still somewhat insulin sensitive despite the hba1c, like you’ve said your lean and probably just need to ease of the cookies lol and then when you retest you’ll be back to the 4.8 you were before
Regarding spillover above, that's readily seen as high triglycerides.