Gravity + angular momentum has the emergent behavior of collapsing distributed masses one dimension at a time:

Clouds(3D) -> Discs(2D) -> Rings(1D) -> Point Masses (planets, stars) (0D)

So flat disc phenomena are obviously very common naturally occurring things. Space is jammed wall to wall with discs and rings.

A flat explosion is certainly interesting, it's not too hard to posit some ways they might come about, but it'll be interesting to see what conclusion their data actually suggests.