Concepts are initial to designing a level, but usually the concept artist is creating the look and feel of the level, and not the design. At least by what I saw in this movie clip.
Basing their design off of the picture they received, it seems like the designers aren’t actually coming up with ‘gameplay areas’ (levels) and are instead just planning a route that they think looks interesting off of artwork. I do the same whenever I look at MC Escher’s artwork Relativity, but that doesn’t mean I actually designed or created a level with gameplay in mind.