The article says that the app only logs when they enter/exit the geofence, not how they move around inside the building. Not to say that they wouldn't want to do that if they could, but GPS location is not really reliable indoors.
Yup. Anything metal messes with GPS. Phones have fallback modes but they can fail spectacularly at times. Even outdoors--sometimes my phone won't navigate sitting on the passenger seat (The GPS constellation guarantees a minimum of 4 satellites above the horizon, it doesn't guarantee 4 satellites in positions that won't be blocked by your car roof.) If you drive onto the property with your phone on your person or in a purse on the passenger seat the geofence might fail to detect it.
There's a boss somewhere who didn't look into this well enough.
