Basenjis' function in the wild is to go after small game. I expect mine to hunt (and kill if they catch them) squirrels and rabbits. Other dogs are a no-no ! Mine know I do not tolerate aggression to other dogs, regardless of their size.
We are just back from a long walk in the forest where my two ran free and hunted (abortively, nothing caught) with a Cocker Spaniel. We met and chatted with lots of other dogs of all shapes and sizes and their owners . Humans stopped to chat, dogs did the normal meet, greet and sniff and there was not a single cross word.
The only trainer mine have ever had is their own pack alpha - ME !
Do not let aggressive behaviour take hold. Nip it in the bud NOW.