You're not entirely wrong, but all's fair in love and war and all that.I gotta say, the princess is really scummy for what she did.
The whole point of the balloon match was so that they didn't attack each other, since he can't hit/injure her unless he wants a death sentence. Despite that, the first thing she does is directly attack him.
I don't know how the classmates feel, but I for sure wouldn't want to have a leader as dishonorable as her.