I have no experience in your field, but I'm very surprised to hear that this isn't worth a phone screen for a 21 year old. Tough industry!
He's just being a jerk to be a jerk.
*not all design people, just a certain flavor
2. "concept art" for a tiling wm makes no sense, because as you point out, it is first and foremost something that is work focused. This is why you build functional prototypes.
Concept art for a tiling window manager certainly does make sense. Especially if you want to define the appearance of one.