Design isn't about drawing pictograms, so nice strawman. The type of design thinking implied in the comment is more about knowing –or at least have the faintest idea about what a visually cohesive system is and could look like. There's no such thing as a "sole developer" in software development because your code is inherently tied to function and that function tied to its design. The more you value that concept the more you "train" your understanding of modern graphic design.