I’m a drone pilot. Drones heavily rely on a number of different sensors, one of them being a compass.
The compass device built into the THETA is probably of a very similar type. Just to give an idea of these, have a look here:
When using a drone, calibrating the compass correctly is critical to flight control. A common mistake is to do the calibration in an environment with ferromagnetic metals, for example on a bridge, near a car or in a building. Even outside on a meadow, there may be stuff in the ground that affects the compass during calibration. In the best case, you get an error during calibration, in the worst case the calibration is done with incorrect data and the drone performs a fly-away afterwards …
And even if the calibration is correct, you won’t get correct data from the compass if used in an environment with ferromagnetic metals. For a drone, this is usually only relevant during start (e.g. from the roof of a car) because in the air the drone is typically away from steel constructions, power lines, etc. But a camera will usually be very near to lots of stuff that may affect the compass, especially when used indoors.