I think it's from looking at artistic illustrations why I think that black holes should be perfectly round / symmetrical, but I'm not even sure if these structures are flat, spherical, or something else!
https://www.astronomy.com/science/ask-astro-blobs-in-image-o...
https://www.astronomy.com/science/blob-of-hot-gas-swirls-aro...
...or the elongation might be due to the fact that it is spinning at 60% of the theoretical maximum:
"Sgr A* is spinning so quickly that it is warping spacetime — that is, time and the three dimensions of space — so that it can look more like a football."
https://www.nasa.gov/image-article/telescopes-show-the-milky...
The thought that an object is "spinning so quickly that it is warping spacetime" just made my day!