The first part of the query checks the Users array for any user that has 'provisioning_managed' set as True. This query alone would return multiple values of 'True'.So, the second part of the query will check the first value returned and because the only values returned are ones that equal 'true' - if it exists, the query will simply say True or False.

Users[?provisioning_managed == ] | [0].provisioning_managed ==