I don't know that there is an "official" accepted explanation. I seem to recall past explanations saying they were waves of star formation. But it does look like the xitter poster is citing someone else.

I think it's an established theory drawing on known variables (we know there are asymmetrical orbits) and the poster is simply demonstrating the inevitable effect.

Nope, there is no "official" explanation of galactic formation. Mostly because we are still in the process of building models that explain their movement and taking measurements to compare those models against.

We still have unexplained phenomena collectively called Dark Energy and Dark Matter which make galaxies behave in a way we don't expect. There is currently no accepted explanation of these. We don't know if these two are an actual thing or if our understanding of gravity is just wrong at that scale.