If you read the book you would not call it advertising material. It's very open-minded and it's honestly not a book that is designed to sell you on Pivotal PAS in any direct way.
The first line in the first chapter is more like an "ok, full disclosure, this is advertising material" but if you read the full text, the Pivotal suite of tools is hardly mentioned. It merely paints a picture you can understand to demonstrate that some kind of platform is definitely needed for basically any enterprise of nontrivial size. (Now if you want to read the real promotional material, get yourself a copy of "Cloud Foundry the Definitive Guide")
This book is only advertising in the sense that if its message is delivered successfully, you will concede that you should use a platform, and we will both agree on the meaning of the word platform. That's it. It's only a bit of tongue-in-cheek first since Pivotal actually makes such a platform, that it says on Page 1, "our platform is the best and only platform" – the rest of the book isn't at all like that.
But if you take it in context for the date of publication, it might make more sense that it was framed this way. Obviously it does not pre-date Heroku. It is a different platform than Heroku. But it is a platform, and a cloud-native one. It's an example of "why you might not need Kubernetes." Also might help to note that this book was published in 2016.
It might be (read: definitely) harder to assert in 2019 that there really isn't any other platform worth considering (than CloudFoundry in 2016), but for a medium-large enterprise in 2016 I'm honestly not so sure. Kubernetes was still new on the scene. People in 2016 in large part still needed to be convinced that such a platform was needed, or even possible, since few existed in the wild/open source commons. (Name your favorite platform that is older than 2016, if you still are in disagreement with the thesis. There are sure several right answers, and I seriously don't doubt this at all.)
To take the contrary position to the extreme a bit, present company including the original poster I think nobody serious (I hope) is suggesting "you may not need Kubernetes, and there is also no serious contender which you should consider in the race for a thing like K8S that you may need for your enterprise, either." Even the original post recommends something instead (Nomad). There is a decent chance you are already sold on this idea, if you're reading this article.
The central argument isn't that you should definitely pick Nomad, it's that you really do need a platform that works for you, even if it only gets you 80% of the way there. The author of "Maybe You Don't Need Kubernetes" started out explaining why Kubernetes just wouldn't work for them. The book, just like this article, comes off a bit like "hey, why not this product instead of whatever it is you're doing there."
But just a little. I strongly agree myself – "In 2019, pick something, anything. (Even Nomad) Just don't do nothing."
These are far from the only two options available.