Jogging in Gym vs Jogging in the Open

This is a delayed posting. Just wanted to share what I have found out last week.
It was my routine jogging day and planned to go East Coast with my colleagues for our regular jog. But it was raining heavily @ East Coast and we decided to head to our company gym.
Before the jog, I forgot to test my glucose level but I did remember that I had a slice of bread 1 hour before my jog. I ran for 30 minutes on the treadmill and it records a 4.17km. That's the usual distance and timing if I were to run at East Coast.....
After the run, we decided to head for dinner......before my dinner (which is ~ 50 minutes after my run), I tested my glucose level..... got a surprise! My meter read 16 mmol!!!
I recalled my CGMS readings that on my running time, my glucose level will actually drop....so, what happened? Guess, I did not do something right again..........
This week i will be going east coast for my regular jog (cross my fingers it wouldn't rain again) and will remember that i need to test before my run........