I just saw a new camera angle and watched it in slow-mo (1/15 sec) I do not believe Artest should have went into the stands, but the suspension vs. what happened is incredible.
Artest never hit anyone until hit was hit in the head by the guy in the hat. He ran right to the guy he thought threw the cup, grabbed him by the head and took him to the ground. At the time other fans and it looked like maybe coaches were holding him back and would have gotten things stopped. While these peope were holding Artest back, a guy (who had previously been pushing Artest off of the guy he tackled) dumped a drink in Artest's face. That was when Jackson arrived in the stands. He did not hit anyone on his way up the stands either. It also didn't appear that he was going to hit anyone in the few moments between when he arrived at the "scene" and when the "fan" through the drink in Artest's face. Jackson did throw a punch at the guy that threw a drink on Artest, but then Harrison and someone else got up in the stands and held Jackson back. Now at this time Artest is being kept from doing anything and so is Jackson, but for some reason the guy in the hat starts hitting Artest. Artest takes a few swings at him and then gets out of the stands. Jackson changes his focus and goes after the guy that hit Artest. Fred Jones had tried to reach over a couple people and grab the guy as he's hitting Artest, but he starts to get hit in the back of the head by Ben Wallace's brother. Ben's brother had gotten out of his seat earlier when the on court fight started. You can see him standing behind the scorers bench at the players are yelling at each other. You can also see what appears to be an assistant coach go up to him and try to get him away from the area.