well you can't just say this and not elaborate!!!!!!!!!
Okay so my interpretation of the event is entirely based off this section of Bill's backstory:
He mentions wanting to be "a star", which feels like a double entandre. He wants to literally escape the confines of his dimension and become like the stars, but he also wants to be "a star" as in famous and adored.
A lot of my vision hinges on the "it was time to put on a show" line. I realize that could mean any sort of big, attention grabbing event (and thats assuming Bill is being honest here), but paired with the star comment, I've always taken it LITERALLY.
I read the event as Bill doing some kind of perfomance that ends with him showing off the third dimension to Euclidya at large. Personally, I've always imagined a magic act. Bill performs tricks and spectacles that create wonder and confusion due to his ability to interact with this third dimensional space, and his final trick is to literally pull himself out into the third dimension.
The actual destruction I'm less sure of. My inital thoughts were that witnessing something so alien and un-comprehensible literally destroyed the people around him. Think people going blind after seeing an angel or the true face of a god.
The mention of mandibles and family matters does make me wonder if perhaps the destruction actually came from Bill unlocking or developing sudden powers related to the new dimension. Maybe he destroyed his 2D body and became a being of pure energy without fully grasping how to handle that. This part is up in the air for me, I think there's lots of fun potential.
I'm not acrually sure what the general consensus is on how Bill destroyed the dimension and how intentional it was? But I remember talking with some people a while back (same people I was talking to about his age actually) and their opinions were a lot different from mine. I think most people seem to think the backstory Bill provides is exaggerated to seem more intentional than it really was, but idk I think it makes sense for his desperate desire to be seen and adored to overrule the logical thoughts that may have otherwise prevented the tragedy.
