>>34214578imo NotSana was lying about her being healthy.
I've always felt that Sana had a bit of a complex about her back issue, probably because that shit can permanently fuck up her art career, and she sees herself as independent/free so she doesn't want the back thing to come off "as an excuse".
Most normal people would've been VERY open about such a disastrous health issue because the adoration and well wishes of the fans would at least help them cope.
But Sana never mentioned this until her fans were getting super worried about her not streaming at all, and even during graduation, never used "health reasons" and asked Cover to keep her reason private.
I think she dislikes getting pitied because of this, I know some very headstrong people who have the exact same mentality about disabilities. They'll say "I'm fine" when asked if they need help, and even if they visibly struggle to do so, will try to accomplish getting up, walking etc on their own.
So when Sana graduated and the regular stream of people started to find her roommate, I think it hurt her pride because she assumed people were watching her out of pity or something, which is why she tweeted out that she was "healthy". She obviously isn't, her stream schedule speaks for itself, but she's too prideful to just "accept help" because of it, and wants to shoulder that burden herself.