I think it's less about how the stories interact(they don't) and more that Nyx announced she was moving the Erynn-Ethan timeline forward and Elena was amongst the characters whose storylines are being pushed back so that the Ethan thing can be resolved.
It would be the final insult to Elena fans
They were both passed out drunk, i did consider that maybe she confused who she was sleeping next to... but then Elena would have a different kind of remorse(she had none, everything was normal for her).
Only getting worst when she figures that she hit the wrong target.