Can it be modeled by a sphere passing by? Can it be modeled by comets passing by?
Imagine that a very long and narrow triangle like this began to move in front of a star:
At first, the tip wouldn't cover the star much, but as the wider portions moved in, the star would slowly appear dimmer and dimmer. Then. as the back of the triangle moved across the star, it would quickly go back to full brightness.
A sphere wouldn't do this; the rate at which the star got brighter at the end would mirror the rate at which it had gotten darker at the beginning.
This is literally all they're saying when they say it's behaving like a triangle. No arcane astronomy sciencemagic involved.
Could it be explained by objects like comets? Sure, if said objects began passing in front of the star in a drizzle, increasing slowly to a downpour, and then cutting off. A cloud of comets of
triangular density, if you will. The problem is, why would a cloud of stuff have triangular density?