Mmm.. Just tried this on my car and nothing happened until I opened the door.
Lexus-tech.eu for my car only mentions while the auxiliary battery is connected, even if the power switch is off, the brake control system activates if the brake pedal is depressed or the door courtesy switches operated. Therefore when servicing the brakes do not open/close the doors or depress the brake pedal if the auxiliary battery is connected.
I would imagine there would be an additional warning about approaching the vehicle carrying the key fob, if what you say happened?