The whole premise of the piggyback is that it cannot modify the actual mapping tables in the ecu. It relies on the hard coded mapping tables of the OE ECU to run the power train because it doesn't have any of its own.
What it effectively does is intercepts certain sensor signals, like MAF and or boost pressure, etc, which the ecu utilizes to calculate fuel flow rate to command injector pulse widths. Or it may modify knock logic to allow for more timing or change the bypass valve strategies for more boost. These are just examples.
So the JB4 intercepts what the ECU really sees, spoofs the signal so that the ECU will command more fueling or allowing more timing from Burger's tuning strategy. This is just the basic principles of piggybacks, I cannot say what BTs tuning strategies are or what they manipulate to accomplish the power gains.