He is extremely confident and that is why sometimes he says some weird stuff for example that he could KO the Klitschkos.
I do not think he is arrogant or he makes excuses.
Since the beginning he said that Cain was the better man in that fight. As for his knee injury....it is not news that plenty of fighters have injuries and almost all of them talk about it.
He is not saying "I lost this fight because I overtrained and I had personal issues". He has said many times that Cain did a great fight and used the right strategy.
Not only brazilians can do this stuff