Try a little imagination; the kenyan student and his brother Omar, photographed together. When might that have been taken? They both look older than they might have been in 1964 when the kenyan student departed from Boston - and Omar also seems more than 19 years old, as he would have been in 1964...so it would seem, as Omar never showed up again in the village in Kenya, and the family described him as 'lost' - The photograph dates from the kenyan's visit to the US in 1970-71 and is of the same period as when you see him with zero at the airport in Hawaii.
The result? Omar wasn't lost. They all knew where he was. And when she was old enough, Zeituni also went to Boston. And that's why, when Zeituni was found, they also found Omar.