I got a more direct case of rejection. 12yo me, at new school, 2nd week of classes, one of the girls that I thought was very pretty was asking others who they fancied. Once she came up to me, I meekly replied "You". I got a very loud and angry "I HATE YOU!" as an answer. Up to this day, more than 20 years later, I have no fucking clue to any possible why, in her mind, I deserved that reply.
You got that reply because you surprised her and her immature 12 y/o brain spat that out as the best response on short notice. It's entirely likely that response had nothing to do with you in particular.
I don't think it was a tsundere, given that during the rest of the year she avoided me and I noticed at least two times were our eyes met, she frowned then looked away. We had zero interactions during the rest of the year.