My 95-year-old FIL, now in memory care, used to tell the legend of there being a full-blooded Cherokee somewhere in his ancestry in the mid-late 1800’s. When my wife got her ancestry.com DNA analysis it suggests that there is no native American lineage. We mention this to him and he says “Well, I don’t know about you, but I have Cherokee ancestry!”
I really do not know why this topic could surprise anyone. You create an incentive for certain behavior, and lo! that behavior increases!
My family has a few stories that don’t add up, but sometimes family stories are repeated so often that they’re accepted as fact.