The filters give more control. Having ?search= would make things more understandable, ?search = ?filter returning all items in the database, a generic search you could say. ?search-files = ?files-filter (but you don't have to filter folders out with folders-filter=\), search-folders = ?folders-filter (but you don't have to filter files out with files-filter=\).
I also like how we have the option of recursive and non-recursive search, and this is where the terminology crosses over, without ?recursive, you basically FILTER the current content on the page, whereas using ?recursive acts more like a search of the database.
I like how we have the control to search files, folders and both. I see the progression this feature has had, and essentially it is only ever going to be used as a search, but then it isn't a search but rather a filter of the content, i guess you could say we are stuck between terminologies.