I cannot see that clearly in those videos but wasn't it an elbow? I didn't see him use his fist, I see him throwing an elbow like he is trying to clear space and catching the guy in the face with it. In looking I can see how the league will call it incidental but excessive contact and fine him $15k or something with no other repercussions, if even that.
Edit: I went and watched a couple of angles on youtube. It is definitely an elbow, and directly after LeBron holds out his hand and walks toward Stewart as if to see if he is ok. Nothing menacing in LeBron's approach. No matter the damage, the diva will get nothing out of this.