I can't see anything wrong with assuming that any vehicle that is powered by electricity should qualify. Depends how they word the clause in their supply contract (probably buried in their Terms and Conditions somewhere), but logically an electric bike or scooter could, within the broadest definition, be assumed to be an EV.
Looking at the Octopus website, all I can find is this definition, which seems broad enough to include ebikes and electric scooters:
The moral issue is the one that bothers me, as I find it hard to be critical of anyone for lying if I were to lie myself. Bit like when I got my hair cut a couple of days ago. I got a £2 discount for being a pensioner, but that was just taken on trust by the barber - I could have been under pension age and lied to get the discount, but that would have been fraud, plain and simple, obtaining monetary advantage by deceit.“EV” means electric vehicle.