You could be right, Flavio. Also the leather loop at the back of the sheath reminds me of Manding knives.
But, if it's not a circumcision knife, why would anyone want such a small knife ? Perhaps a woman's knife ?
Ik know the women of the Mangbetu tribe have small daggers for daily use. They have the same shape as the daggers used by men, only the size is different (much smaller).