Do you know the reason why he was so confident when fighting against me?

I remember there was a boy named Arunesh in my class in 7th and 8th grade. In 7th grade, he used to be nice to me but in 8th grade, he started being mean to me. I remember he was also a target of the bullies in my class and he used to often be in fight with my enemy Arjun and few more bullies and he used to always lose and not dare to really fight against them. But Arunesh used to not be scared of me and try to pick on me. I used to fight him too but he could beat me most of the time. I remember we used hold our hands and try to wrestle each other and he could most of the time overpower me. In short, he wasn't scared of me at all like he was with other boys. Honestly I was bigger built and taller than him and could have defeated him but the problem was that I used to sit and fight whereas he used to stand and fight because many times other boys have punched my balls while standing so I used to avoid standing while fighting and others could win against me. I also asked another boy that why Arunesh is so confident to fight me whereas he is usually not confident against other boys. That boy answered me saying "That's because you are a coward" and laughed and I used to feel embarrassed getting defeated by even weaker boys like Arunesh.