Without more context it seems hard to make conclusions from the data presented.

In terms of the raw figures both Daily Active Users and Monthly Active Users are up. However Monthly Active Users has increased at a faster rate than Daily Active Users, therefore user engagement which is defined as the ratio of daily active users to monthly active users has fallen.

Is this because existing users have reduced engagement with the platform, while Facebook continues to signup new users, or is it because the new users Facebook is signing up are not as engaged in the platform, or a combination of both?

For example maybe Facebook is 'hacking' its user growth figures by signing up marginal users at the cost of engagement.