Broken Surprise!

Last night at about 10 o’clock my parents heard a “BANG”. They didn’t know what it was though. They thought it was a wooden board that had fallen out of place under my bed. They checked my bed but they were all there, so my dad checked the rest of the house from top to bottom. But my dad couldn’t find anything so he went back to bed. When he awoke today he did what he usually did, got dressed, went downstairs and opens the blinds to the deck. When he did open the blinds there was something wrong! The left panel of glass was cracked from top to bottom! When my mom came down she thought it was rain until she looked closer.
They didn’t know what had happened but they thought it was shot by a BB gun, because they found what they thought was a point of entry.
But it was weird because it was as if it were shot from the inside so they didn’t know what it was. Then my neighbor said it could have been that there was a crack and the gas that was it broke through the crack and shattered the glass without it falling out. So now we are getting a guy to come out and put a new window pane in the door.