I often run both Strava and RideWithGPS on the same phone.

And they give results that frequently vary by a few percent. I've seen Strava create zigs and zags that just don't exist with my riding.

For Strava, some of the Garmin devices are only accurate to 5 seconds, which can create interesting results for short segments.

Anyway, I'd trust the wheel mounted induction device over the GPS device, if properly calibrated. But, as mentioned above, does it really matter?