The Storage graph is notoriously inaccurate, and the Spotlight database determines those various categories.
One method that you can use to make that graph more accurate is to rebuild the Spotlight database.
There's a simple terminal command to do that. But, I use a simple method in the System Preferences/Spotlight pref pane.
Click on the Privacy tab, click the (+) button, then add your hard drive.
Wait a few seconds, then select your hard drive from the list in that pref pane, and click the (-) to remove it.
Close the pref pane.
The Spotlight database will start to rebuild, which will take anywhere from 5 minutes to a couple of hours, depending a lot on the speed and size of your hard drive. When the rebuild completes, you will see much of the Other is gone, redistributed to some other categories (colors)