GD weird result question

So yesterday was my first full day checking my sugars, so I don't know much about how I react to things yet. But I think my number last night was very weird.

I tried a pretty high carb dinner: cole slaw, tofu, 2 biscuits (white bread) with peanut butter and a few cherry tomatoes. The biscuits were the high carb part obviously, and they by themselves were pretty much a whole meal's worth of carbs according to my dietician's instructions.

Right after dinner I took a short walk with the dog (not far, not fast). Then I accidently tested at about an hour and 20 minutes instead of just an hour.

My number was only 90! That's what I'm supposed to score when I wake up in the morning!

????? Was it the walking? The testing 20 mins too late? Were they magic biscuits??