It doesn't matter but it's an interesting Official Scorer question.
You have this rule:
10.18(d) No run shall be earned when the runner's advance is aided by an error, a passed ball, or defensive interference or obstruction, if the scorer judges that the run would not have scored without the aid of such misplay.
Originally I assumed the unearned was Cairo because he advanced home aided by an error. But the O.S. obviously ruled that he would have scored later in the inning anyway.
Then you have this rule:
10.18(c) No run shall be earned when scored by a runner whose life is prolonged by an error, if such runner would have been put out by errorless play.
This seems to clearly apply to Jeter because if they successfully converted the force he's out.
But here's what I think happened. There is no Fielder's Choice unless an out is successfully converted. They attempt to get the out on the force at 2nd but with Kennedy's throwing error Jeter advances to third and Cairo scores but Williams becomes the unearned run because he is the one who reached on the error. He did not reach on an FC becuase the FC never happened.
Bernie Williams reaches on force attempt, throwing error by pitcher Joe Kennedy. Miguel Cairo scores.
10.18(b) No run shall be earned when scored by a runner who reaches first base (3) because of any fielding error.