I'm just taking a shot in the dark here.
It seems to me that the plants look a bit odd because the nodes are intermittent. In the veg stage you get 2 leaves, then 2 more leaves a node higher etc.
When a plant goes into bloom the nodes become intermittent. So instead of 2 leaves at a time you get one at a time. That's what gives bud sites that zigzag stem appearance.
It is quite possible that the creators of these cuttings took them from a plant that was in flower and reverted them back to the veg stage by turning the lights back to 18/6.
This would keep the intermittent leaf production. Perhaps it might begin to revert to 2 leaf veg nodes in time. I'm not sure on that as I never experienced it.

Anyway, there is my 2 cents on this matter. Maybe I'm right, maybe I'm wrong... who knows. Maybe someone else might have a definite answer. I'm just going on what I see.

Take care.