i am not sure what the origin and exact meaning of the term 'linked_meta' is, but I would guess that it is a term created for area 51 meta sites and the implied meaning is clear.
Perhaps stack meta enjoys a different life than a lowly autogenerated linked_meta site, but i would submit that stack meta should be tagged as such in the interest of consistency and to facilitate programmatic handling of the /sites response, e.g. for sorting.
otherwise, we can simply ignore the site.state field and check the endpoint for '.meta.'
Is there something I am missing?