LARNACA, Cyprus — A man described as “psychologically unstable” hijacked a flight Tuesday from Egypt to Cyprus and threatened to blow it up. His explosives turned out to be fake, and he surrendered with all passengers released unharmed after a bizarre six-hour standoff. As more became known about the motive of the 59-year-old Egyptian who was taken into custody, authorities characterized the commandeering of the EgyptAir jetliner, not as an act of terrorism, but more like a “family feud” with his former wife. The aviation drama ended peacefully on the tarmac of Larnaca airport on the island nation’s southern coast with the surrender of a man identified by Cypriot and Egyptian authorities as Seif Eddin Mustafa. The incident was likely to renew concerns about Egyptian airport security months after a Russian passenger plane was blown out of the sky over the Sinai Peninsula in a bombing claimed by the Islamic State group. But Egyptian officials stressed that their security measures were not to blame, and there was praise for the EgyptAir flight crew.