Yeah, that will likely be his argument but the truth is that they are in a conspiracy to commit a crime. This was, unlikely, not two independent crimes. A race requires multiple participants in other cars or this would simply be speeding.
The people in the various cars decided together to race one another on the streets of Georgia and that decision to commit the crime of street racing, resulted in a death.
As an FYI, there is a famous case for just how little sympathy courts (traditionally) have for people committing crimes where two people went to rob a liquor store. They did not even have a gun but they pretended to have a gun (object in pocket or something) and the clerk pulled out his gun and shot one of the assailants.
The other assailant was charged with murder in the commission of a felony.