A human knowing anything about the gems is highly far-fetched, 
1: No way of learning about them since there is no written history of it
2: Finding a temple and actually surviving in it is also unlikely, the gems nearly die in there own rooms sometimes
3: If any other gems had survived the Canon characters would know about it because of Garnet unless they were recovering like Aqua

Sooooo... No, I don't think anyone would know much about what happened except for Aqua and Blood