This is happening a lot now since Strava set up their auto-flagging system.  When he opens the activity on the mobile app, the first page he sees should have two buttons right at the top that say “ride” or “ebike ride”.  Click “ride” and it will set it as a ride.  Hopefully that will fix it.  I have heard that some people are not getting that option though.  If you don’t see that option, maybe try changing the activity type to something like a run, then change it back to a “ride” or “mtb ride”.