Thanks a lot Josh! I watched that a long time ago and completely forgot the part about Instancing a Collection .
The instance indeed comes in with an Empty:
And by the way: scaling by negative 1 is not the same as mirroring; it has the same effect when in Object Mode, but I use it quite a lot and when you are in Edit Mode this trick tends to flip the Normals. Easy to fix, but just something to be aware of.