Yeah this advice really isn't good. IF is proven for a reason because science has shown that after many hours of not eating, your body starts burning sugar and fat stores; insulin spiking isn't the problem here. In fact, this type of dieting schedule is CLOSER to what humans are natively evolved to do; constantly snacking throughout the day is exactly the kind of thing that keeps spiking your insulin and never letting your body start to burn fat, which is what makes it hard to lose weight in the first place. This chapter pretty much has it completely backwords which is... yikes.
This is not to say however that the keto diet is on par with IF. While IF is natural and also accepted in pretty much any scientific circles, Keto is definitely a fad with mixed results. It's not bad, but it's not exactly great either, and the more important thing is that for most people it's not sustainable.