That is 100% Cap’s Avengers (Age of Ultron/Civil War) suit with the star ripped off, and maybe it hasn’t been washed for a while. We don’t know if he’s been in Wakanda the whole time, or if he left to do his own thing after leaving Bucky in their care. The trailer kinda hints at the latter (BP welcoming Rogers back).
Why would Shuri start churning out Black Panther style suits for a bunch of ex-Avengers when their own armies don’t even wear that tech? It seems likely they’re reluctant to give their most state of the art combat gear to outsiders, even someone like Rogers who’s earned T’Challa’s trust.