World Rugby, who were also asked to review a similar incident in a match between the two teams in London last year, found insufficient evidence after a review of video footage and audio, and submissions from players on both sides.
The Springbok hooker believes Curry misinterpreted his instructions to teammates in Afrikaans, which have a similar sound to the alleged discriminatory language, in the tense 16-15 victory in Paris.
"I think it is a very sad thing when you live in a first-world country and you think the rest of the world speaks English," Mbonambi told BBC Sport Africa on Tuesday.
"It was unprofessional on their part. They could have gone on a website and looked for an English dictionary and for the word in Afrikaans. People (in South Africa) understood, but obviously their side misunderstood.
"I'm glad it was well taken care of and that is all in the past now. But I have never racially swore at him."
World Rugby conceded Curry had made the accusation in good faith, but the outcome infuriated England's Rugby Football Union, who said they "fully support Tom Curry in raising the racially abusive behaviour he experienced".
Curry and Mbonambi both received online abuse in the aftermath of the match, which drew stinging criticism from both teams.
As it happened, Mbonambi lasted only three minutes of South Africa's 12-11 victory over New Zealand in the final after leaving the field with a knee injury.
