Unfortunately for the embarrassed Israelis, he was the local green grocer - not the head of Lebanon's Hezbollah group.
Leah Tzemel, the Israeli lawyer who obtained their release on Monday, said Israel had snatched the four Nasrallahs and their neighbour on August 1 in a commando raid in the Hezbollah stronghold of Baalbek in northeastern Lebanon.
The army apparently believed he was related to Sheikh Hassan Nasrallah and could be used to pressure the leader.
Tzemel said: "He [the grocer] was brought here and interrogated and very quickly they understood that they were taken for no reason.
"Then they [the Israeli authorities] just put them in jail and held them."
The Israeli military had no immediate comment.
The Nasrallahs told Tzemel that 24 hours of questioning exclusively focused on any relation they might have to the Hezbollah leader.
But Tzemel said it became clear to the Israeli security services that the five have no political or religious ties and are not related to the leader, who hails from southern Lebanon.
The Nasrallahs were detained
during a raid on Baalbek
In an appeal early on Monday to Israel's supreme court, Tzemel said she argued that the Nasrallahs were being held "hostage to be used as a bargaining chip for negotiations".
By Monday afternoon, the Nasrallahs and their neighbour were driven to the Israel-Lebanon border and returned home, she said.
In all, 15 people were killed in fighting in the Baalbek area on the night of the raid.