From a quick google it seems like both Mo and his brother were sent away to another location in Africa by his birth mother - where they were given new names. Mo was then sent to the UK.
I’d be surprised if the people who made the BBC documentary didn’t also ask that question.
The problem is it seems very not to be the truth and the surname thing is the biggest problem.
If he wasn't born Farah why does his whole biological family in Somalia have that surname? And his twin brother?