Kyle looked plenty mature to me.
Harvick got into him about 4 times within 1 corner and 1 straight. Kyle was done and spun him out. Boys have at it. Harvick throws a tantrum like he always does, charging people on pit road, Kyle said no thanks, and drove off. Harvick is the one who left his car unmanned and in the middle of the road. Was it dangerous, yeah, but they're both equally as responsible. Kyle drove off, because boys have at it is designed to remain on the track. Kyle was very calm, didn't insult Harvick or his wife, explained his side to the camera and comes away with a solid 11th place finish, that moves him up 3 spots in the standings. He did the mature thing.
The immature thing, would have been to get out of the car and fist fight with Harvick, then hurl insults into the camera like an angry kid. Sure, the fist fight would have been a lot more manly, but not the mature, Championship thing to do.
I'm not a fan of either of them. I don't think Harvick intentionally got into Kyle, but he did regardless, and from the driver seat all you feel is 'bump, bump, bang, slam' think WTF and then retaliate.