"Dude… what the fuck"

I swear to god this ending of the chapter makes EVERYTHING in the game take new context. Especially since I can't figure out how/why they'd make the first dark fountain if they're the knight. Unless I was right the first time and the reason they say Asriel isn't returning that book is because Kris is hiding it, but how did they know they'd end up in the closet? and why can't any darkener recognize them? Even the king, who ostensibly fought the knight in person. There's just so much to ask!