There is never going to be a clear cut answer of how close is too close with regard to a crowded sprint. It is much more similar to baseball in the sense that players enforce unwritten rules.
A pitcher can throw a warning shot at a guys head, and while not against the rules, everyone knows what's being communicated. But one centimeter to the wrong and the ball hits the pitcher, then the rules spell clearly that the batter takes the base.
Bennett may have tried to throw the warning/deterrent shot, but was once centimeter to aggressive. Batter, take your base. Rest of the world, move on and get ready for the next pitch.