Yeah, everything is learned from the Soul Crystal. From page 217 of Encyclopedia Eorzea Vol. I:
This is backed up in game, with some Job Quests concluding with a line about attuning to the Soul Crystal. There's also other knowledge gained from the Soul Crystals, with one obvious example being Fray. Despite the real Fray being dead, our Darkside manifesting as Fray was still able to explain the origins of the Dark Knights. In the White Mage Job Quests, a simulacrum of the long dead A-Towa-Cant appears from the Soul Crystal. There's a lot going on with Soul Crystals, transcribing skills, spells, memories, and even simulacrums of past owners. Don't really need a teacher when the WoL is incredibly gifted and capable of mastering all forms of combat, not to mention the Echo that may help them see into the souls and memories stored in the Soul Crystal.Ever since the height of the Allagan Empire in the Third Astral Era, the practice of using crystals to store and impart knowledge has been prevalent in Eorzea. An adornment known as a "soul crystal" is worn close to the skin, where the uncommonly clear facets of the carefully cut shard catch and transcribe the ebb and flow of a soul's aetherial composition - effectively capturing an imperfect echo of the wearer's memories. This arcane tool engraved with the myriad deeds of heroes from eras past was employed by many of the disciplines of yesteryear to preserve and pass on the skill of successive generations of masters.
The wisdom contained in a soul crystals, however, is not so easily drawn forth - an untrained neophyte cannot simply pick up one of these gems and expect his mind to be flooded with the knowledge of advanced spellcraft or combat techniques. Without first attaining sufficient proficiency and tempering one's soul to mirror the maturity of the crystal's contributors, a prospective student will be denied even the slightest glimpse of enlightenment. Thus, as is the case with the more contemporary disciplines, the key to mastering the secrets of a soul crystal lies in diligent study and training.