Eunho wasn’t too interested in sparring with the general because he didn’t want Yuna to be suspicious of him or feel threatened by him. Eunho had trained in both his past life and in this life. He grew extremely strong because of his training and experience. In reality, he was stronger than Yuna’s father, but he didn’t want her to find out.
He was just getting used to being around Yuna, but she could grow suspicious of him in the future. He didn’t want her to misunderstand. Yuna was very smart, and he didn’t want her to find out that he knew her from his past life. She would think he’s crazy. Afterall, it was impossible for him to already know how to navigate the battlefield and fight enemies at a young age.