I don't think you need to treat an NDA as a blanket 'you can say absolutely nothing'. The post is 90% about his own preparation process, and 10% about the day-of schedule for interviews. The schedule of the day-of process is not exactly a secret, everyone that has interviewed at Amazon went through something like it. The recruiters should be telling you what to expect before you even get there. It's not like he gave a hint as to what the questions were.

Here's the thing, posts like this are just making searchable what many people already know. The difference is that the tribal knowledge of how to get through interviews is one of the reasons why our profession has a diversity problem. If you don't know that you should read those books and plan for those questions, how well do you think you will do? Plenty of this wisdom travels over beers among the circles of friends in the industry, but putting it on the internet democratizes the knowledge for everyone.