There is still a difference
"Garmin devices run a calculation during recording to total up your moving time, or the time you are not resting/stationary. This moving time is divided by total distance to get average speed. When your data is uploaded to Strava, a separate calculation is run based on your GPS data to determine moving time. This can be different than what your Garmin reports. If you see differences in Average Speed between Garmin and Strava, first check your stats for moving time and total distance as that should explain the differences. "