Hmm.
My guess would be the photo could be edited.
Why? Look at the shadow of the garment wearing archer, look how it seems to hold 2 bows (or maybe there are 2 caracters).
Minimap also doesn't show what we see in the field.
It could be a bug or some camera tricks (notice how the 2 degree armor wearing glaive girls have the same name, same armor, same character, same everything and the frames in which we see them suggest that photos were taken in every frame and she's simply walking). Why do I think that? Because if we gather 10 people and we recreate this picture where they walk behind each other their walking animation wouldn't be syncronized (like in this case!), every armored character has a walking animation syncronized with the one behind it.
Same goes with the horse riding guy in the back, etc.