It is getting power from the battery, via the starter/solenoid lug to the alternator terminal. The other wire going to the passenger compartment is feeding "something", but not sure what, by using that alternator terminal as a bus. I do not think that is why the car stalled. It should run from battery voltage (if it is sufficient voltage) even if the alternator output ceases. It is hard to tell in a single video. If you can get it to consistently repeat, see if it does it by keeping it in first (or second if you have a manual body), it might be torque converter clutch, or maybe throttle closing without anti-stall dashpot. Did your fuel pressure change at all? And do you have an all time vacuum gauge installed? If so, that might help with "seeing" what the vacuum is doing.