S1·E14 Yahiko's Battle

Yahiko, the sole student of the Kamiya Dojo, has started to step away from his training from time to time. He says he's merely going on a walk, but it is clear that he takes his swordsmanship training very seriously, and it doesn’t look like he's ditching to slack off. Curious about what he's doing, Kenshin, Kaoru, and Sanosuke decide to follow him. What exactly is Yahiko's reason for ditching?