I hope you realize that parents, country of schooling, accent and nickname have zero bearing in regards to citizenship.
Can you source Almeida's "admission?"
If you feel that strongly about a dual citizenship, why was the prior proposal of two flags removed?  Additionally, why fix this one page only but not the other 5 UFC-event pages on Wikipedia listing him as American?
Personally I feel you've violated the rules here by insisting on something that you merely assume (Brazilian citizenship).
Bruce Lee was the child of Hongkongese parents, raised in Hong Kong but that doesn't make him not American.
Mel Gibson is the son of an Australian, raised in Australia, but we all can agree he's American.
Same thing here.