Strava has privacy controls, use them. Don’t accept friend requests from strangers etc etc.
If it wasn’t Strava causing your bike to get nicked it will have been map my ride, or Facebook, or twitter, or motion-x or garmin or any other app out there. But then maybe some unsavoury type saw you washing your bike on the drive the other day, or cycling home, or there’s someone searching the insurance database for nice bikes to pinch. I’ll not go on, you should have got my point by now.
Oh and buy a big chain to lock your bike up in the garage, they might be able to get in, but don’t make it easy for them to leave with your bike.