Yea, a sibling did a DNA anaylis and it doesn’t match what we know (our family history is well understood due to people tracking it since the 1700’s.)

Most people in the US with my surname come from a very small set of immigrants (3 or 4) from about 1700-1800.

The thing is, my genetics are heavily influenced by who each generation married. Easy to see just on the US tree how quickly genetics mix, and it’s not like those immigrants were purely anything either.