The [[ikiwiki/directive/inline]] directive generates a form if
it has either rootpage, or postform with a "yes-like" value. This
means that

    \[[!inline pages=... rootpage=sandbox postform=no]]

does have a form. I would expect it not to (although
mentioning rootpage there is useless).

See also [[forum/How_to_disable_"Add_a_new_post_titled:"_submission_form?]].

--[[smcv]]