No one except you knows what you have on your disk.
Those categories are rather volatile and should be taken only as a rough estimation of disk usage.
If you want to explore what's taking up your space, I recommend DaisyDisk, which will give you a graphical layout of all your files and folders sorted by size.
That graphic gets its data from the Spotlight index, and when that index is corrupted you will see bad readings like you have there.
Run the command below in Terminal to reindex Spotlight and that should straighten you out. Give it time to complete the reindex. On a larger drive it can take an hour or so.
I have solved my problem with this method. Thanks. If you cannot understand the command line, you can enter: sudo mdutil to learn the usage of this command line firstly. Then you can use it easily.