Anything that says "powered by clean master" I distrust. But system storage menus are often problematic: in order to make things "user friendly" they hide or mislabel information.
In any event, that screenshot is only showing a small part of the storage. I don't know whether there is more stuff below it if you scroll down, but usually they have some category like "system & other", "other files" or "Misc files" as well. Of those descriptions (all of which are real, and mean the same thing on different manufacturers' phones) "system and other" is the best description: what they mean is "all space used by the system plus all other files that don't fit into this small number of classifications we've shown above".
If scrolling down doesn't show something like that then I'm afraid this CM-powered system tool is even worse than I'd expect something developed by Cheetah Mobile to be. If it is there but off the bottom of the screen, where many people won't guess to look, that's a pretty poor design anyway.