Rather it's likely the OS doing the best it can to handle the URL for you. The OS has a mapping between the URL and the bundle identifier of the app, and apparently looked for the bundle on a disk that happened to be attached, after it didn't find it on your main disk. Which is perfectly reasonable in itself.
Looking at multiple application directories is one thing but executing things from the backup directory is another.
> but executing things from the backup directory is another.
Time Machine backups are structured in a very non-proprietary way. Each backup is just a folder, protected from modifications, with hard links used to save space. If anything, I'd say good on Apple for supporting a backup format that works exactly like making a copy of a folder.
Do other apps launch from backups like this? It’s very strange.
My expectation is that if I want to go back to a backup I have to restore that backup first then run the application. Executing from a backup is surprising and frankly difficult to reason about. What version is even running? How would I know?