http://revach.net/article.php?id=3125

Section: Taryag Mitzvos   Category: Minchas Chinuch
A Goy Needs A Unanimous Decision

The Minchas Chinuch says in Parshas Yisro that the Din that we follow the majority or Rov, is one of the Taryag Mitzvos and it applies only to a Yisroel and not to a non-Jew.  When a Jewish person is brought to Din the Torah teaches that we follow the majority, if the majority of the judges find him guilty he is punished even if a significant minority of the judges find him innocent. The Rishonim teach us that a Rov is a regarded as a Safek, however it is a Geze’iras ha’Kasuv that even though it is a Safek we follow the dictates of the Rov.

Therefore, although a non-Jew is put to death for transgressing one of the seven Mitzvos Bnei Noach he is only put to death if the judges unanimously find him guilty. If it is a split decision he is not put to death because it is regarded as a Safek, and the Din of following the dictates of a Rov doesn’t apply to a no-Jew.