King Limhi, being a just man (Mosiah 19:17), caused that additional wine than their tribute required to be given to the Lamanites, which Gideon had just recently told him of his plan. For this to work the people would have been making additional wine for themselves beforehand, as it takes one to three months to make wine. In
addition they were only commandment to import of half of all they poses not to
make something specific for the Lamanites (Mosiah 19:15).

Mosiah 22:10 And king Limhi caused that his people should gather their flocks together; and he sent the tribute of wine to the Lamanites; AND HE ALSO SENT MORE WINE, AS A PRESENT UNTO THEM; and they did drink freely of the wine which king Limhi did send unto them.