See [[en:Wikipedia:Village pump (technical)#Moving without redirect]].
The ContentHandler code correctly realizes that it cannot create a redirect for content models such as "js" or "css". But the Special:MovePage user interface does not reflect this: it will still offer the option to leave a redirect behind, and after moving will incorrectly state that a redirect was created. It appears the API action=move will have the same problem, including 'redirectcreated' in the response even if no redirect was actually created.
At least the part about incorrectly stating that the redirect was created should be fixed.