Ringyoku never sent Riboku off his horse.
Kaine got shot by Koku'Ou and Riboku was trying to dismount and save Kaine but got intercepted by Ringyoku. But even so, Ringyoku didn't even beat Riboku, and Riboku was more worried about saving Kaine than beating Ringyoku lol.
Then when Riboku is trying to get on his horse, Ringyoku sneak attacked Riboku from behind. If Riboku was fully focused on Ringyoku, Riboku would have mid diff Ringyoku.