No it was literal. Some people just never accepted the obvious intent.

: Ancient humans existed
: 100,000 years ago, period. We weren't some space-faring conquering race.

Apparently we were in the haloverse. Or at least the Forerunner humans were.

: We just happened to be the place that the Librarian liked and the species
: that fascinated her.

Nope, we were Forerunners. Sparky said so, Joe Staten said so, John Candland said so, etc, etc, ad infinitum, adnauseum.

: There may have been something done during re-seeding
: that allowed us to reclaim the Forerunner Mantle from the depths. It's
: almost like we inherited something. There are many, many places you can go
: with this story and with gameplay, especially with the inclusion of the
: evil Didact that could provide the Didact far more depth, not to mention a
: chance to really knock the human story out of the park (either showing
: human success or another failure at the Mantle, give or take a select
: heroic few like the Chief who live up to it or represent what's best in us
: all, blah blah trope-y stuff).

No, we were Forerunners.

But that's all pre 343.

Now we are a separate species with a deep genetic similarity to Forerunners (whatever that means). The more primitive Forerunner condition is to have 5 fingers. And modern Forerunners were genetically modified and could mutate their bodies into different forms as they went through life.