Have you at any other time have had Garageband on your mac, if and you deleted the Garageband app on your mac but you will not have deleted its libraries of instruments and sounds which will still be on your mac. You cannot delete the default apps that come with the mac, so don't try.
The problem you have is that the Spotlight index has been corrupted in some manner which is giving you the erroneous Storage result, no amount of deleting items will change that.
So the article I gave you is pretty self explanatory all you do is open System Preferences> Spotlight> Privacy
then drag the icon of your Hard Drive into the Privacy pane. At this point we will deviate from the article, close
System Preferences. Now Open System Preferences> Spotlight> Privacy, highlight the Hard Drive icon and click on the minus button to remove it. This should force Spotlight to re index. Click on the Spotlight icon in the menubar
and enter a word, try Images. If Spotlight has started indexing then you should see a progress bar under the word
you typed in.
If that doesn't work then try this, open Terminal (Applications/Utilities) type in this command
sudo mdutil -E /
press Return
enter your password
this should force Spotlight to re index so check again that it is indexing by typing a word into Spotlight.
If you want an accurate account of the Storage space on your mac use this free app, https://www.omnigroup.com/more