Minecraft – Will this spawn slimes

As Ben Blank said, the only thing that will spontaneously cause an explosion, if you haven't made any TNT, is a creeper that got into your house. I see three possible directions for the creeper to enter from:

1. The caves

   Most likely, either you have an insufficiently lit patch of floor in the connected caves (walls and ceilings don't matter), or there is a dark branch that you haven't found. I strongly recommend always installing doors at connections between caves and living space.

2. The front door

   The damage you described seems to be focused around the doorward side of you. You say you removed "the bricks leading up to the door", but if there is still a one-block-jump path it is possible a creeper got in anyway. Next time, don't worry about removing the path, just close the door! If you have a wooden door, zombies can break them - this will cause a loud sound of someone punching some wood.

3. The ceiling

   You haven't said anything about your ceiling design. Is it possible that your ceiling had a hole in it through which a creeper entered? There are [minimal spoilers] ways for dirt/grass blocks to go away, so if you had a dirt roof perhaps a creeper fell in.

Miscellany

To my surprise, it appeared that nearly all my objects were still there. Most were sitting in the same spot that their chest was in. As best I can tell, I was able to recover nearly everything, with the exception of the signs and 2 of the 5 chest blocks.

Chests drop their contents when destroyed, as you saw. If there had been two explosions, then the second one would have destroyed all of your resources, as they have almost no “health”.

They also tend to leave big craters, and there seemed to be too little structural damage in this case.

The size of an explosion crater depends on the strength of the materials. If you meet a creeper outside, then it will leave a large hole in the dirt, but the same explosion will do much less damage to stone.

Oddly, the door and torches outside were gone, but the structure itself was untouched save for two holes in the floor (marked "Gone" in the above picture).

Wooden objects are generally weaker against explosions, and torches have no blast resistance at all.

The Mob Spawning section of the Minecraft Wiki goes into some detail about what the requirements are for a mob to spawn. The parts relevant to this question are:

• If it's not a squid, then...
  • the spawning block itself must be non-opaque and non-liquid
  • the block directly below it must be opaque or upside down slabs / stairs and may not be bedrock
  • the block directly above it must be non-opaque
  • the spawning mob must not be obstructed by solid blocks, other mobs or liquids

There are other conditions on Slimes, but those are concerned with them being in the right chunks, rather than the precise blocks. So yes, for every non-squid mob the game tries to spawn, the mob needs to spawn on top of a solid block, with the block they spawn in, and the next one up, being non-opaque non-liquid, and with the block they spawn in being air so they don't fail the collision check. They will not spawn in mid-air.

Recommended practice for spawning slimes is a wide, flat floor, in a chunk they can spawn in, below level 40,