The explanation is a simple one and the new messages aren't invasive
You may have noticed that in recent weeks random tweets started to appear in your timeline that weren’t exactly messages any of the people you followed wrote, but rather tweets they favorite.The feature came with no formal announcement from Twitter and no mention about it whatsoever by any of the company’s leaders.
Well, Dick Costolo finally stepped in and explained what it was all about. It seems that when you pull to refresh twice and get no new tweets from the people you follow on each occasion, you’re going to get some of the messages these people favorite just so there’s some new content in there.
Twitter has been planning to start displaying tweets favorite by people you follow and popular tweets from people you don’t even follow, but it hasn’t exactly specified exactly how this was going to happen and how they were going to show up in people’s timelines.
The decision wasn’t exactly well-received, as people were angry that Twitter was trying to force feed them content that they had no interest in.
With that idea thrown out the window due to the harsh attitude users had, Twitter seems to have adapted a bit so that users wouldn’t exactly get mad. Therefore, it’s only delivering favorite tweets of the people you’re following only if there are no new messages to show. This means that there’s a very high chance that people who follow hundreds will never even see this new feature in action.