Hi all!

So after finishing act 2 I was left with strong impression that Nightsong, Ketheric Thorm, and basically all that shadow curse business are somehow tied to events of bg1 and/or bg2. Naturally I didn't play previous games and I kinda don't want to sink some 300 hours into them, but bg1/2 story recaps on youtube don't seem to mention any of these characters (well except Jaheira and Minsc). Neither they are mentioned on wiki.

Am I missing something here? Is act 2 tied to some bg1/2 dlc? An adaptation of some tabletop module? Or is it all just original Larian lore?