What caused Equiano to think the white men were evil spirits?

From the text:

I was immediately handled and tossed up to see if I were sound by some of the crew; and I was now persuaded that I had gotten into a world of bad spirits, and that they were going to kill me. Their complexions too differing so much from ours, their long hair, and the language they spoke, (which was very different from any I had ever heard) united to confirm me in this belief. Indeed such were the horrors of my views and fears at the moment, that, if ten thousand worlds had been my own, I would have freely parted with them all to have exchanged my condition with that of the meanest slave in my own country.