If I said 'screw you', and that cause you to flip out and kill everyone around you, you couldn't say the root cause was me saying 'screw you'. The root cause might be childhood trauma, extreme emotional imbalance, irrational thoughts, etc. The statement 'screw you' was the trigger.

Similarly here, a trigger might be uploading a photo to FB, but the root cause of an issue might be a bug in encoding JPGs.