You don't need a Thermodynamics Ph.D. to understand this. Moreover the normal (gas) cars have the same behavior. So it's annoying that a car expert don't know it.

You get the best mpg at a constant speed of ~50mph, and it's better with the cruise control because it reduce the times that you need to accelerate or decelerate.

If you go too fast, the mpg drops because you need more fuel to compensate the additional resistance.

If you accelerate and brake (for example in a city), the mpg drops because you need more fuel to accelerate and when you brake the energy goes away as heat.

The advantage of the regenerations brakes is that some of the energy that is "lost" as heat braking is stored and used again to accelerate. This is not magic. It doesn't make braking lossless, it only recycles part of the energy so accelerating and braking is not so bad (it's only bad). This is well known for the electric and hybrid cars (I think that there are some tries to do something like this for gas cars, perhaps store the energy mechanically, I'm not sure.)

I think that the recommendation was (paraphrase) "If you are going to drive inside a city, it's better to turn off the cruise control."

The articles that he understood something like (paraphrase) "It's better to drive inside a city than in a highway with cruise control."

It's very surprising that a car expert can understood this so totally wrong that it look like it was a willfully misunderstandment.