One of the ז מצות בני נח is דינים. According to the Ramban on parshat vayishlach (34:13)
the laws that were counted [as one] of the seven commandments that the Children of Noach were commanded is not only to set up judges in each and every town, but [rather] He commanded them in the laws of theft and fraud, abuse, fair wages, laws of guardianship, rape and seduction, the main categories of damages, injury to ones's fellow, laws of the borrower and lender, laws of purchase and sale and similar to them
It means that the non-jews have to make laws about man to man transgressions. One of his examples are theft. So according to this, why is there a separate issur of גזל as one of the ז מצות בני נח, if it is included in the mitzvah of דינים?