OK, first I went overboard (intentionally) and went with the Create Samples tool, for estimation and validation streams, and the Model Comparison tool, for, well, comparing models. It was fun but fruitless when attempting to recreate the data found in the answer.
When I went back to actually following the instructions I had to change the Tool Version (right click on the Predictive tools) and to get my output to match the answer.
I had this one done in well under 10 minutes but then spent over an hour trying to figure out why I was getting the wrong answer. I finally gave up and started checking solutions and all of them were giving the same wrong answer. Then I find out that the DecisionTree tool has changed. @JoeM please put a note in the instructions for this challenge warning people to change the version number before attempting it.