Evidence?
No wait, let me get it for you.
The goobbue. "THE" Goobue. This particular goobbue model. If it said "A" goobbue mount, you might have more footing to your argument, which presently falls flat.
I can go one step further, and contrast models summoned by the items:
Goobbue Horn vs Laurel Goobbue Horn:
Note its not the same mount, in the same idea that the Legacy Chocobo is not the same mount as the Grand Company Chocobo. Different item, different mount.