I think Garmin Connect counts my runs in steps and therefore steps in calories ... and then adds calories to that for the run.
For example, I start my morning run with 150 active calories and run about 10km, GC estimates that I burned 800kcal during this run, but in Garmin Connect I have 1650 active calories, so Garmin adds 600kcal.
I dont have connected any apps to GC or even on my phone.
Any ideas why it looks that way?