You don't say exactly on what you are double-clicking, but the message seems to indicate you are clicking on a music track or album. This is normal behavior for iTunes.
Maybe you didn't realize it, but you had an "Up Next" list filled with music. You can see this list icon (looks like 3 numbered lines) to the right of the "what's playing" box at the top of the iTunes window. If you interrupt this list by double-clicking on another song or album, you will get the message you saw.
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.14.x,; iPhones, iPods and iPads galore!