How could this be? You'd think that if two people were related to a couple of hundred people in common they'd have to be related to each other. The reason it makes sense that they are not related is once you go back enough generations to find a common ancestor, every one of the three people you are comparing have so many ancestors that it's easy for two people to be related to that one famous person but it is pretty long odds that they're related on the same line of ancestors.
Take our relation to Harry S. Truman. I am related to President Truman through my Müller/Schach line in Nürtingen, Esslingen, Württemberg and Truman's mother's father's mother's father's line. My wife is related to Truman on her Cunningham-Rose-Bridge line and Truman's father's father's father's father's line. Finally, my wife's friend is related to Truman on her mother's father's mother's mother's line and on Truman's father's father's father's mother's line. It's easier to see it than to read it.
|My wife's connection to President Truman|
|My connection to President Truman|
|My wife's friend's connection to President Truman|
It really comes down to the exponential increase in the number of ancestors with each generation. After only 10 generations, you have over 1000 ancestors just at that generation, plus nearly 1000 when adding every ancestor in every previous generation.