Again we only observe gravity, we do not understand where the force even comes from. Yes we understand the effect of gravity in great detail, we just cannot recreate the force in any equation what so ever. No one knows how to make gravity.The statement has more twists than a pretzel. "Don't know the first thing" except what we know (GR and the standard model), which is a lot. .
A black hole is vacuum; it's not "made" of anything except spacetime curvature. There may be objects inside it that have fallen in, but unless and until they are close enough to the singularity for tidal gravity to tear them apart, they're no different from objects anywhere else.I see BH as popped neutrons and other atomic elements broken down.
A BH can't explode. The time reverse of a BH, a white hole, is not the same spacetime geometry as the Big Bang.I would guess if a BH exploded the cooled particles would form atoms again from the debris much the same way we see in the BB