Haha, well you better take a break if you're playing it on PC the mod tools come out soon and you'll never be able to look at CG again.
This might help you out though, the member that made the new Saint Mihiel campaign said this about it.
It's defined in the mission as Finkeren said. Waypoint can have several priorities:
High - Aircraft will follow waypoints no matter what happens. They do not respond to enemies at all
Medium - For scouts: Aircraft will follow waypoints, but if an enemy is threatening him he will attack that one first/ For Recons/Bombers: Aircraft will weave & defend with rear gunner but continue to waypoint
Low - For scouts: Aircraft will follow waypoints, but if an enemy is within visual distance (8km?) he will attack that one first/ For Recons/Bombers: Same as Scouts I think.
Looks like the Gotha has a waypoint with "Low" priority.
Also, the Gotha could have an "Attack Air" command assigned, but that would make no sense.