It was a violent time. There were “kill them all” types among the Powhatan, but also among the Jamestown settlers as well. A doctor tried to poison the indians, succeeded with quite a few, in retaliation for an attack. Then, there were those who tried to get along, on both sides.
Opechancanough not killing blacks isn’t necessarily true, there weren’t very many there at all at that point. The headrights system was providing more than enough Irish, Scotch and English indentured servants. Africans were comparatively expensive. They were all indentured servants at that time.
The African slave trade began in earnest for several reasons. Chattel slavery, slavery for life, did not exist as a legal construct until th 1670’s, they began running out of desirable land to give indentured servants once their term had been served leading to the collapse of the headrights system, and plantation owners began to perceive that Africans had a better survival rate due to better disease resistance in swampy, tropical areas like the rice and indigo plantations further south.
All this coincided between 1670 - 1680. Indentured servitude faded and chattel slavery arose from that point onward.
Of course the Spanish had been importing Africans to work as slaves in the New World from the very early 1500s, more than 100 years before the first Africans arrived at Jamestown. The Portuguese began capturing people on the coast of Africa and taking them either to Portugal or to their Atlantic islands to be slaves from around 1441. Of course they were just doing what the Muslims had been doing to non-Muslims (black, white, or whatever) for centuries, and what the Europeans had been doing to outsiders (whether pagans, Muslims, or the wrong kind of Christians) for centuries too.