Twitter has is allowing tweets from users you do not follow to appear in your Twitter timeline.
Normally, a user's Twitter timeline is filled by posts from accounts the user follows and re-tweets from those accounts.
Twitter’s support page explained, 'When we identify a Tweet, an account to follow, or other content that's popular or relevant, we may add it to your timeline.'
The change is seen by some as an attempt to close Twitter’s gap on Facebook in user numbers. Twitter has 241 million while Facebook has over one billion.