I think people interpreted the alternative ending as the real ending in which the whole series was just a fantasy of the writer Taeyoung. I guess it made people feel like they were taken for a ride to be so invested in the couple and then find out that they are only a figment of imagination of another figment of imagination.

I don't use clubbox anymore and because I understand korean, I never used a search engine. Soompi would be the best source however to get clubbox links.