section of "About my mac",
About this Mac is listing everything related to Audio as "GarageBand". If you installed Logic Pro X or MainStage all support for these applications will be listed as GarageBand as well, all Apple Loops, including the loops used by iMovie as sound effects, the instrument library with the sounds for the instruments.
Are you using any other audio applications, that may be needing the installed sounds and loops?
Files used by GarageBand or attributed to GarageBand will be in these folders:
/Library/Audio/Apple Loops/
/Library/Application Support/GarageBand/
/Library/Application Support/Logic/
and in the corresponding folders in your user library:
~/Library/Audio/Apple Loops/
~/Library/Application Support/GarageBand/
~/Library/Application Support/Logic/
Also in the folders
~/Music/GarageBand/
~/Music/Logic/
~/Music/MainStage/