After slaying almost all of Tuifeai's troops, some having run off, they left one alive to report back to Tuifeai that they were here to have him taoiseumu ("cooked in an umu").
After decimating almost all of Tuifeai's troops, some fled, they left one alive to relay to Tuifeai that they were there to execute him as a sacrifice ("cooked in an umu").