Even though the Nephites were preparing for an attack, the siege had weakened Cumeni to the point of surrender, suggesting that the interception of the supply train left them without hope. The Lamanites had captured Cumeni from the Nephites and, naturally, captured its provisions. However, these provisions must have been depleted by Nephite use, especially since the Lamanites could not replenish them by farming. Thus, the Lamanite garrison must have been almost completely dependent on being provisioned from the outside, and had no other options when those provisions were intercepted.
Variant: “Unto our hands” should be “into our hands.” Skousen explains: “And finally, ‘into’ one’s hands, never ‘unto’ one’s hands: the original text was 56 to 0, the current one is 55 to 1. [The original text has 56 occurrences of “into our hands” and none for “unto our hands.” The current text has only this one instance of “unto our hands.”] This is one that the 1920 Committee copy isn’t marked, [sic] it is a typo by the typesetters in Chicago.”