I was watching TV when suddenly a full bottle of strong homemade liquor burst in the cupboard by itself. How was that possible? It was really creepy.
If it was fermented, then there may have been active yeast still producing carbon dioxide. The pressure from this may have caused the explosion.
If it was distilled spirits, the vapor pressure of ethyl alcohol at room temperature is not zero and rises with the temp. And the fluid itself will expand with increasing temp. So if the bottle was absolutely full (no airspace) and tightly stoppered, the expansion pressure may have caused it to burst.