I found this article, it explains that the 2 brothers were in LAX, one had a united ticket to some where and the other had a ticket on ANA to Tokyo.
My guess, both were leaving out of same area, Imran obviously had a domestic ticket NOT associated with a NEEDED passport…probably to GUAM….
His brother ABID had the ticket to Tokyo…
At last minute, IMRAN boards ANA flight as ABID.
SOMETHING along these lines happened.
https:// www.japantimes.co.jp/news/2017/12/28/national/tokyo-bound-ana-plane-returns-los-angeles-passenger-wrong-flight/