I guess that's the nightmare of any CI, finding out that some ancestor just screwed up their lineage. However, you should investigate more and even make a DNA test, who knows, after all it might have been a fabrication by your remote family to make them sound "exotic".
In any case, now you cannot be certain, and I dont know if you ever will. But you should not despair, but accept that you cannot change anything about it. Think like this, there is nothing in this world you can change about what are God's plans for you. If you were after all 100% white that's because it was all part of His will and plans, but if you're not, well, then it was never meant to be.
I think everyone wondered at least once whether by some misfortune, some non-Adamic blood infiltrated in their lineage. For instance, if I came to the discovery that I had some non-Adamic blood running through my veins, I'd be completly devastated, for it would strike at the very fundation of my beliefs. But that cannot change the truth and neither the future. If that were ever true I don't know what would hurt me more, the fact that I am not his child, that I won't live forever, the fact that I won't see Yahweh and stand by his side, that I'll never see the glory of His kingdom. That's so painful to think of
, but again, it's not we who decide, but God.