You are correct that Amazon has the capability to control FireOS since it is a fork under the GPL. But they won't do it. Amazon will never add any substantial content to FireOS because they would have to provide the source code to the public (and back to Google). Amazon is not interested in operating systems. They will accept what Google gives them. That's fine but it's not what the author of the article was implying. In fact, the author does not seem to know what an operating system is.
Asking simple questions is one of the context specific tasks I was talking about. But that's a pretty shallow use. Just try to drill down and ask a more specific question in response to the first answer. Alexa: "The next full moon is on Tuesday." "Will that be another super moon?" "Will it be cloudy then?" "What is the exact time of fullness?" Alexa will have no idea.
If people you have given computing equipment to are getting good use from it, I'm glad. I'm not saying Alexa or voice operations are useless. But this does not suggest that Amazon has conquered the world. And that is the fallacious premise of the article.