Slaves require training and whenever they disobey their mistress there are consequences. Mistresses also distribute punishments at their discretion and it is more to do to molding you to be a better slave and to test your limits. After all being complacent and not pushing yourself is unacceptable.

Slaves should have already learnt about the mistress they are serving and as such as this slave hasn't, Mistress Kiana is going to punish him.