Even electric-assist road bikes have wider tires than their non-assisted counterparts. For example, the Bianchi Aria-E comes with 28 tires; the regular Aria comes with 25s.
As Leisturm said (or wrote), when you add a motor and battery to a bike, you need wider tires to compensate for the additional weight -- how much wider depends on how much weight the drive system adds... in the case of the Aria, Orbea, etc., that additional weight is < 8 pounds, so a relatively small increase in tire size is sufficient.

In short, everyone is right. And let's keep our tires round in the new year!