Personally, I'm not sure that being gluten free is the issue, rather than being free of the heavy carb foods you were consuming that happened to contain gluten.
I too am gluten-free. My coeliac panel was inconsistent, but then I had been low carb for a long time beforehand, so by the fact I wasn't eating any bread or baked goods, beer or drinks containing barley as examples, meant I was gluten-light. My Aic was low 30s before going completely gluten-free and stayed pretty mcuh the same since. No material changes down or up.
To be frank, I think your success has been linked to eating better, easing on the drinking and giving up smoking, and sticking with it..
Whatever worked for you, I commend you, but I can't totally buy gluten being the sole key.