If you've worked with them at all, you know that bipolar junction transistors are not symmetric -- if you put them in your circuit with the collector and the emitter reversed, then they don't behave the same as if you put them in the right way. Hobbyists know that the schematic-diagram symbol always has the arrow on the base-emitter leg, and the arrow points from P to N.
But the BJT diagram in this article and in elementary textbooks is symmetric -- there's no physical structural difference between the collector and the emitter in the picture.
This isn't necessarily bad, simplifying the problem to illustrate the fundamentals is a legitimate pedagogical technique.
The "obvious" question is, what else is going on in real devices?
I think the answer is that actual commercially-available discrete BJTs are fabricated on a planar substrate, the same way they're done for integrated circuits, and then cut out of the wafer and packaged for individual use. In this process, the collector (I think?) is generally the lowest layer on the wafer, and is much larger than the emitter, which is on top, and is generally much smaller. In the planar case, there's an obvious geometric asymmetry that explains the device's asymmetric behavior.
I'm not 100% solid on that explanation, and I don't recall where I saw it, but this is the kind of next-level detail that I would have liked to see from the article.
(Minor edits for clarity.)