BG1 and 2 used 2e, of course. Whilst FR was a world available for AD&D, it was not the official homeworld but just one of the options. The difference was that, whilst later editions used FR material (races etc) as canon for the game, the earlier ones only did so when playing in that setting. By using FR as the official setting, 5e is making all the FR stuff canon for the game from the outset, so using its races and history as the default.
Yes, the original BG pairing (and the NWN series) was set in FR and so used FR lore.
To answer the add-on question, FR came first. Then AD&D was developed, and then FR was offered as a campaign setting for AD&D.
Last edited by Sadurian; 19/10/20 02:51 PM.
