I should add, when I was trying to boost at the battery, I couldn't get at the actual post because of the red plastic guard, but rather I clamped at the metal ring that is visible on the wire going to the LEFT from the battery. This ring appears to be connected to the wire, but potentially NOT. Also this ring is right before the "black box" before the battery terminal.
Assuming this black box is the circuit interrupter, this would answer a few questions. Also it is possible that the "pop" I heard was this, since it is basically in the passenger side, right behind the wall.
EDIT: I started searching, and it could be due to the "BST" cable.
http://www.bimmerscan.com/bmw-battery-safety-terminal/
If this is the case, it would explain a few things.