I don't believe for a minute that he had a motor in his bike.

But if anyone does develop a suitable motor, i.e.:
- Silent operation
- Undetectable controls
- Completely contained in the bike's tubes
- Light enough (motor and transmission and battery and controls and mounting) that it makes sense to carry the weight for the length of a classic, with it being dead weight most of the time

Then that manufacturer would make a lot more money putting it into production. Plenty of bike commuters would buy one.