Okay, on second look, I admit that there were shards that look exactly like the boards Twilight was using to seal the hole and nothing at all like the wall even before any boards actually got broken, so I suppose strictly speaking you might be right.
But that does not change the fact that if Dash had made a second hole, there would still be boards over the first hole, and the shards created when she flew out through the second hole would be shards of wall rather than shards of boards. So we can conclude that nothing that could possibly have happened actually could possibly have happened.
I can only roll when others walk. It is my nature to take jokes seriously and serious statements in jest. And the cruel irony is that I am powerless to stop it when I do it consciously; never shall the ability to stop meet the knowledge that there is anything to stop.