Finding things in Finder · Finding what was moved
Why does an app show my file's location as the external drive instead of its usual folder?
Short answer: Some apps follow the shortcut and show where the file really lives — your external drive. It's the same file either way; keep opening it from its usual folder, or use Move back if you'd rather it lived on your Mac again.
Some apps follow the shortcut and then display where the file really lives, so they name your external drive rather than the original folder. Both refer to the same file — it's just two ways of describing one location.
It doesn't change anything about how you work: keep opening files from their usual folder, and saving goes to the real file on the drive.
If you'd prefer an app always to see the original folder, move that item back with Move back in What's Using Space → Relocated (N).