I think people are confused, this has nothing to do with gmail as far as I can tell.
Google is going to websites and subscribing itself to their newsletters. This is not related to consumers.
It's still good to move away from gmail and google in general, just pointing out that it's not scanning your gmail inbox or something like that.
This has nothing to do with gmail or the emails you send/receive.
The process is googles search bot will subscribe google to marketing newsletters available on websites, it's outlined in the linked post: "Google will either subscribe to your emails automatically or you can add marketingemailtogoog@gmail.com to your email lists and that will do it."