Selphie may have forgotten (and probably did) the GF's appearance, too, but I just don't see it as feasible that the Tonberry is the GF in question, when nothing was indicated that it was anything anyone in the party had met before. There would've been some sort of moment where she thought she remembered something, or the Tonberry would have remembered her, or something.

The guy in Trabia is just kind of funny. It's weird to think how to actually take that, considering that it's supposed to be a direct joke of his playing FFVIII, but I tend to just take it as the joke it was intended to be.

Really, though, I just think it's much more likely that it's some GF that we never meet. It's not as if the sixteen GFs you can Junction are the only GFs in the world.