It could be any number of techniques. Though, given the rather consistent lighting across multiple characters, I'd say it's some mix between the roof/ceiling being turned into an emissive or a large emissive plane/ghost light rotated 90 degrees or so downward toward the floor(s).
Render "e.png" looks to be using a warm, large spotlight with the render emitter on (hence the white window) or perhaps a large emissive plane, and the closeup shot of the guy looking out the window is likely a ghost light with the same temperature or a spotlight with the render emitter off. Some of them (namely the first and last renders) look like they could be using the in-built lighting that came with the environments.