If you’re doing a procedural map, baked lighting would be tricky - so yeah dynamic GI is likely the way to go.
And yeah, very high indirect lighting would create those soft shadows due to it basically turning the walls and floors into huge surface area lights.
I wouldn’t assume that specific effect means GI must have been used - but it would be good evidence for it. I’d have to take a closer look, but all of that stuff can be faked. Regardless, you’ll probably need to make it work with dynamic light either way for a procedural.