Seems more like twitter banned the author 9 years too late.
It is definitely an immature tweet, however I think 9 years can change a person a lot. Maybe twitter could have given him a warning about his tweet and ask if he would like to delete it before the instaban algorithm hit
That raises a bunch of different questions about what Twitter are doing to change history, and the way they represent their platform, but those are separate to the banning of users based on their history.
Besides, this might be motivated by Twitter acting on a complaint. It could be that Sarah Palin (or someone representing her) complained about the tweet recently, in which case Twitter need to deal with that now.