So this was an HbA1c test, or a fingerprick test, or were they sending off a vial of blood merely to get a BG result, ie the same result they could have done themselves with a fingerprick, or what was it? I don't understand why you'd want it to be 'fasting' for any of those?
It can't possibly by any stretch of the imagination, affect your HbA1c whether it's fasting or after you'd just eaten half a ton of doughnuts. This test doesn't measure your BG right now, it measures how much glucose has stuck to your red blood cells over the last 10-12 weeks - this can't be affected by your BG right this minute - only what is has been over the past couple of months.
The ONLY blood test you're ever likely to have in companionship with diabetes would be a fasting Lipids tests, so they can measure the HDL and the Trigs properly. They never measure the LDL anyway, that's always calculated from the HDL and Trigs figures, so they need to be correctly measured so all the numbers can be relied on.