@D.S.
ADS-C can send route data either on a periodic basis or if changed:
Predicted Route Group- Latitude at next waypoint
- Longitude at next waypoint
- Altitude at next waypoint
- ETA at next waypoint
- Latitude at next +1 wpt
- Longitude at next +1 wpt
- Altitude at next +1 wpt
If so equipped and engaged the a/c could send this data w/o pilot knowledge. ADS-C update with info listed above would be sent from plane to ground automatically when the pilot changed the next or next +1 WPT.
I'm not saying this is what happened. Just saying that what has been reported is possible.