I think Spyro was the first mainstream game to standardise achievements, you could do random stuff in-game and it gave you a little pop up, carried over to Ratchet and Clank and now every game has official achievements
This. They were indeed called Skill Points, and Insomniac loved to tie cheats and bonus material to completing them. I played the shit out of Spyro and Ratchet and Clank back in the day.
Not the first one on the PSX, that's for sure. Also, getting some extra stuff for 100% a game wasn't new by the time of Spyro, both Donkey Kong Country and Crash Bandicoot already did that