Someone who was there and happens to be a driver (Tyler Graves) said the opposite:
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http://www.motorsport.com/sprint/ne...their-take-on-tragedy-and-defend-tony-stewart
http://rochester.twcnews.com/conten...-could-not-have-avoided-hitting-other-driver/
Another 2 drivers who happened to be there defend Tony Stewart (#45, which is the car right in front of Tony, and another driver who was a few cars behind Tony). They say it's very possible he saw him in the last moment, and that he could have used the throttle to try and avoid Kevin.
As for facts, there are a couple. Kevin Ward Jr. stood in the middle of the track. Tony Stewart's car hit him and killed him. And that's about it. Those are the only known facts to the public, so far. Even Stewart pushing the throttle is an assumption (a well-founded one, maybe). The rest is speculation.