A few users have noticed it in the past few weeks that tweets from people they don’t know have started to crop up on their timeline. Now, it would seem to be an official policy that Twitter will be showing you tweets you haven’t really asked for. It would seem Twitter already updated its FAQ section to make it clear that you won’t just be getting tweets from people you follow. It is basically like the sponsored or promoted tweets you have been seeing on your timeline but without anyone being paid.
This is the section Quartz is pointing out about this policy: “Additionally, when we identify a Tweet, an account to follow, or other content that's popular or relevant, we may add it to your timeline. This means you will sometimes see Tweets from accounts you don't follow. We select each Tweet using a variety of signals, including how popular it is and how people in your network are interacting with it. Our goal is to make your home timeline even more relevant and interesting.”