konqueror can only tell file types from the extensions?

I used KDE3 a long time ago, and then KDE4, so i might be confused.
I have the impression that KDE3 could tell a file type with out 
depending on the extension. Right? I did something wrong with the 
config, or didn't install a package? The preview of folders is a KDE4 
thing too?

(Linux mint 18.2 mate 64bit)