While Brixton may be engaging in clandestine behavior befitting a spy, his most notable feature is his powers and those are what is highlighted by referencing Superman.
Plus, “I’m the black James Bond” doesn’t quite roll of the tongue the way “I’m black Superman” does.
The black Superman line in the trailer, along with the first look at Brixton’s abilities signaled that the rules no longer applied and that the Fast & Furious franchise would now be dabbling in superpowers.