De acordo com a IGN:
While it might seem strange to pit Shang-Chi against a villain most
commonly associated with Iron Man, this choice backs up a popular
theory that the Mandarin will be depicted as Shang-Chi's father in the
MCU
movie.
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The problems here are two-fold. One, Marvel no longer has the rights
to the Fu Manchu character. Not only has this made reprinting the
early Master of Kung Fu comics difficult, but it's also prevented them from
referencing Shang-Chi's parentage in subsequent comics. Two, Fu Manchu
is now widely criticized as a racist caricature and an example of the
"Yellow Peril" storytelling trope. Even if Marvel could bring Fu
Manchu into the MCU, it's doubtful they'd actually want to use a
villain with such a problematic history.
Então Shang-Chi e Mandarin não estão relacionados nos quadrinhos, mas Mandarin substituirá um personagem que a Marvel não pode (e provavelmente não deveria) usar.
Observe que eles estão se referindo ao mandarim "real" (revelado no one-shot da Marvel Todos saudam o rei), em vez do "falso" interpretado por Ben Kingsley.