i think as the revs drop slightly for a second when a drain is put on the electrics, they may have dropped too low and thus causing you to stall. As said above see if you can do it again. I bet you cant.
There is a switch then when you activate the higher amperage elctronics components that will tell the ecu to open the butterfly ever so slightly to compensate for the extra load from these such as rear windscreen heater AC etc... its not unknown for those switches to fail (iv seen a similar situ before) but where they are and how you replace them im not sure
May have just been a one off as said i bet you cant do it again.
My bet is not enough revs additional load from powersteering pump and air con, engine stalled, the end lol.
There is a switch then when you activate the higher amperage elctronics components that will tell the ecu to open the butterfly ever so slightly to compensate for the extra load from these such as rear windscreen heater AC etc... its not unknown for those switches to fail (iv seen a similar situ before) but where they are and how you replace them im not sure
May have just been a one off as said i bet you cant do it again.