Read up on (or chat with) auto designers. Material choice absolutely plays a role in what shapes are possible. Steel body panels are generally made via sequences of stampings, and complex compound curves and fine intersecting forms are very difficult to do in steel. This is why Audi talked up their engineering around hydroforming and welding. It enabled new forms in metal that weren't achievable previously. Auto designers have a love/hate relationship with the engineers, as they both enable and snuff out good designs.
Carbon fiber cloth let's you do more, and carbon composite castings allow for pretty insane shapes more reproduceably. This guy may be talking out of his ass, but the assertion that composites enable more aerodynamic design flexibility is in line with industry expert statements.