Firstly, well done on your weight loss and lower blood sugars - a drop from 66 to 41 in 4 months is terrific.
Your diagnosis back in June of 66mmol wouldn't have been false or a spike. A spike lasts a relatively short time - an hour to 3 hours usually. The diagnostic test was an HbA1c, which measures your average blood sugar over the preceding 2 to 3 months. Normally on diagnosis you have 2 HbA1c tests close together, the second one to confirm the first, or a fasting blood glucose test. Did you have this?
I suggest the excellent reduction is down to your diet and weight loss, with a bit of help from the Metformin. If you wish to stop the Metformin have a word with your nurse/doctor first.