O.K. Actually the Russian Wikipedia explains it:
https://ru.wikipedia.org/wiki/%D0%90...82%D0%B0%D0%BD His real name was Amet Sultanovich Amet-Khan, Sultanovich being his so-called patronymic name (indicating his father's name), but as he registered for a flying course, he gave his name in accordance with the Tatar tradition, that is, his patronymic name first, and that led to a misunderstanding and his father's name, Sultan, came to be used as the pilot's name too.
It's a pity it didn't occur to me to read the Russian Wikipedia article first... or this information may have been recently added to the article.