How is this hadith understood?

Recorded in Sirah al-Nabawiyyah and Mustadrak al-Hakim : > I am a black man who is black, foul smelling with an ugly face. If I fight these people until I am killed where will I be. He said "In Paradise". So he fought until he was killed. > The Messenger of Allah said "Verily Allah has whitened your face, made > your smell pleasant and increased your wealth. Al-Qaeda leader Hamad bin Hamoud Al-Tamimi used this hadith as evidence that "blackness" is a disease which can be removed from martyrdom. How is this hadith/tradition supposed to be understood and what is it's authenticity taking into account the chain and text?