I can think of a few ways it could be done:
- they could have painted the shadows on the floor
- they could have put an “area light” just below each ceiling
- they could have marked the floors as “don’t cast shadow” (which in Unreal is un-marking them from “cast shadow”)
- they could have rendered the entire thing in parts, and then composited it
Generally, there seems to be very few “real” shadows – the people cutouts seem to have mostly a bit of reflections on the floor, not actual shadows.
My first approach would probably be to make nothing cast diffuse/specular (“directional”) shadows, and just use ambient occlusion and a skylight. Set the distance for ambient occlusion very low, like 100 centimeters, to avoid ceilings getting caught up. See where that takes you.