Batteries are cheating, no doubt about that.
But I'd always rather have another cyclist on the road than another car. I guess cars are cheating too.
If batteries on a bike is cheating then cars are in their own, special, super over-the-top, 10x Rosie Ruiz level cheater category. But yes, when spontaneously racing Ian batteries in a bike is cheating.
Full disclaimer: I own two bikes with batteries. Neither are throttle-controlled, however.
It was unclear from Ian's account whether the other person was even aware of Ian. It sounded more like someone on a reasonably green motorcycle making a delivery.
E-bikes are fantastic devices: a bicycle that is assisted with a motor, rather than a motorcycle augmented with human power. It's remarkable how much a 100-250W boost can enable a casual cyclist.
I think the chap noticed me when I passed him and politely remarked to him that "he was cooking!" Had the lad been riding purely under his own power, I would have been put to shame.