Boaz is introduced at this point in anticipation of the major role that he is about to play in the narrative, namely, as a husband to Ruth. From the Tonga kinship perspective, however, he is on the wrong side of the family—that of Elimelech (i.e., patrilineal descent).
If this had been a Tonga setting, Boaz would have had to come from among the dead a Tonga setting, Boaz would have had to come from among the dead husband’s mother’s relatives, i.e., from Naomi’s line (matrilineal descent).

Source: Wendland 1987, p. 172.