WHUTUPORO is Maori for "football", which, in turn, means "rugby" in New Zealand. It has nothing to do with African American culture and the word itself actually derives from the English word. The Māori vocabulary is parsimonious; almost all possible short words are meaningful, making clear pronunciation of the vowels essential, unlike English. Hence whutuporo is a phonetic interpretation of "football".
whut up BRO is a term African Americans use to greet friends. If the T shirt relates to a sports team, whatupPRO would make sense. I don't know what the All Blacks emblem is, but I suspect this is the link.