Disqualified Under A Stricter Law
But Gezi and his family are a special case, because they're descended from a group of Ethiopians whose Jewish ancestors converted to Christianity under pressure in the 19th century. They're called the Falash Mura. They secretly practiced Judaism but were not allowed to emigrate with the other Ethiopian Jews until a hard-won political compromise a decade ago.
Even then, Israel didn't approve them under the standard Law of Return but under a stricter religious law that says to be Jewish you need to prove an "unbroken" maternal Jewish line. It is under this stricter law that Gezi's Christian great-grandmother disqualifies him. : Parallels : NPR