$fields = get_field_objects(); requires a post ID, if none is supplied then it returns values for the current post. Exactly what that values is depends on the page it’s running. So, the field in question for the current post in your case only has 2 values. These posts have information on how you can get fields in specific field groups.
ACF5
https://support.advancedcustomfields.com/forums/topic/get-all-fields-by-group-id/
https://support.advancedcustomfields.com/forums/topic/how-to-get-all-acf-groups-or-field-for-specific-post-type/
https://dream-encode.com/acf-get-all-fields-in-a-field-group/
ACF4
https://support.advancedcustomfields.com/forums/topic/get-fields-in-a-group-or-tab-for-output/
