Fyi there is (or at least was) a dragonborn sub-race that has tails, so this is kinda wrong. It's purely flavor so it doesn't really matter, but still.
Edit: wait, tieflings also officially have tails, what the fuck are you on about?
...right, maybe I've just forgotten how venn diagrams are supposed to work, but doesn't inclusion of "let's ignore the book description of this race" mean that the op is saying that tails aren't lore accurate? The reason I read it that way is because there are way too many people who insist that dragonborn with tails aren't lore accurate when they can be.
I definitely see where you're coming from. The author excluded dragonborn from the "Many Colors" section, which might lead one to believe that this is a diagram of traits that are commonly expressed in a race despite the official book descriptions. e.g. it's stereotypically common to make blue tieflings or green goblins despite the official descriptions.
So either the author is wrong for saying dragonborn don't officially come in many colors, or they're wrong for saying tieflings don't officially have tails. Either way, it's a bad diagram.
Oh thank god I wasn't the only one getting confused by it.
which might lead one to believe that this is a diagram of traits that are commonly expressed in a race despite the official book descriptions
Yeah, this is pretty much exactly it. It seemed like a chart of things people include despite the lore, which is why I was left feeling confused as shit because, well, tails on dragonborn and tieflings are lore-friendly.