Nahh, it just jammed the signal so he couldn't get into his car without first climbing over it to nobble the transmitter unit. The keyfob system was cryptographic, like modern ones, and wouldn't unlock in response to any old signal. But the electricity meter (and transmitting device) was on the wall halfway down the garage, much closer to the car's receiver than the doorway where you'd operate the keyfob from.
The effect of a flat battery on a car with purely electric door locks left as an exercise for the reader. (I think the AA bod eventually managed to open the bonnet from below using car thief skillz, and an inconvenient Anderson connector was later added to facilitate jump-starting the central locking in future.)