This contextual information is “pulled from across Facebook and other sources, such as information from the publisher’s Wikipedia entry… trending articles or related articles about the topic”. The hope is that this contextual information will give users the information they need to decide whether the link in question is reliable or not.
This is the best move I have seen any of the platforms take in response to fake news so far. This approach provides a non-invasive system which helps people make up their own minds about what they want to believe and share, rather than deciding what is and is not true for them.