It's certainly not a fire sale - that would imply BAe were a financially distressed company who had to sell assets at any price. That's clearly not the case. They've made a strategic decision to exit Airbus at what they think is an appropriate time and invest elsewhere,and only time will tell if that was a good or bad decision.
As to the value they got for it, this was ultimately agreed by audit. If memory serves me well, BAe were originally looking for about £3.4bn but EADS only offered £3bn. BAe weren't happy with this, so they exercised a 'put option' which enabled them to sell to EADS at a price to be settled by arbitration. Unfortunately, the s*** hit the fan shortly afterwards and the price of BAe's stake headed south. They were basically screwed by their own machinations.