It is easy for most of us to forget the power that Nephi had when he was filled with the spirit (1 Nephi 17:48 . . . I spake unto them, saying: In the name of the Almighty God, I command you that ye touch me not, for I am filled with the power of God, even unto the consuming of my flesh; and whoso shall lay his hands upon me shall wither even as a dried reed; and he shall be as naught before the power of God, for God shall smite him). Nephi surely had not forgotten, however.
From a purely human standpoint we can understand how two men (if there were only those two) might subdue and bind a single man. Nephi's second phrase of this verse indicates that Nephi understood that his strength was not always his own, and that the ability of his brethren to bind him had to lie with the Lord's sufferance, a sufferance not demonstrated earlier in the noted occasion.