I'll take a stab.
The test in court for dangerous driving is this:
For driving to be deemed dangerous it must depart markedly from the standard of care of a reasonable person.
Now I do not know the details of the event, but the fact that 1 car lost control and crashed with enough force to kill 2 people would lead me to believe that they were putting the safety of the public in danger.
I believe the defense sucessfully argued that there wasn't enough evidence to show if the person charged caused the crash. It is up to you to decide if participating in the race means being responsible for the outcome. I personally do, much like if you praticipate in a robbery if someone else kills someone, you too are charged with that murder, even if you aren't directly involved. He choose to take part in the criminal action and should be responsible for the outcome.
"It takes a big man to admit when he is wrong....I'm not a big man" Chevy Chase, Fletch Lives.