Well, it's a little harder for people who had no guns, nor wheels, nor Horses to kill millions of people.
Genocide does not require a technological edge over one’s neighbours: In Rwanda it was carried out with machetes.
There is no technological determinism to genocide. Because it is not based on that – it is based on dehumanizing others. Further, genocide is rare, especially on a continental scale.
So while blacks might have wiped out the natives of North America it is unlikely. Because black people are generally are peaceful. History shows that
When Columbus arrived in the Caribbean the people there already knew about blacks: they had traded with them. Africa is much closer to the Americas than Europe. And, armed with iron weapons, blacks could have made short work of the people there if they wanted to.
White ppl are at an extreme end of human history. Defeating your enemy and maybe taking over their country is common. Wiping them out wholesale and taking their land is not. For Whites that does not come from their guns and their bombs but from how they think.