I find the description made by Inigo very unclear. For me it would be high tempo at least. And still it would depend on the lenght of the effort. For me Z2 is the pace i feel i ride and press the pedals but I train by power and I stick with it. But had same concerns as you.
I don’t know the guy, but generally training in one zone will provide one type of benefits and end up in diminishing returns. One can select the focus of the training according to the goals, but it is always good to sprinkle in a small amount of sprint/threshold/strength training.