This is based on three steps of logic:
- Inventory: Stories you have not seen from your friends and the pages that you follow.
- Signals: Information FB has available to make informed decisions about your likes such as:
- Age of post
- Who posted the story
- How fast is your internet speed when accessed
- Type of phone or electronic device you are using
- What kind of content may be problematic to you
- Click Bait
- False News
- Predictions: FB determines how likely you are to comment, share, hide or report each story.
Facebook collects a few dozen predictions then weight them. After, they roll them up into a relevancy score and present posts to your timeline based on those scores.
The stories in your newsfeed are likely to by chronological because the age of a story is one of the determining signals. However, it is not strictly so.