The garden system is a gender system created for to describe their gender without having to use binary terms such as "masculine" or "woman-aligned". Not all non-binary people use the galactian alignment system.
The theme of space used in the galactian system was chosen because space is genderless, but aspects of it are often personified to have gender for artistic, religious, or cultural reasons. Non-binary people have also historically been associated with space. This is not to be confused with the celestial system or xenogenders, as the galactian alignment system uses the theme of space only as a naming scheme.
The terms are more indications of gender but one may choose to identify as them. They indicate gender alignment, which may not be related to one's actual gender or gender presentation.