He isn't using it to predict far outside the data, for which a polynomial will capture the important trends. 2013 is pretty close to the data, and to 4th order, it does match a sinusoid. So, I'd say it's your fault for trying to apply his predictions outside of the bounds that he did both implicitly (the graph) and explicitly (the 2013 quote).

There's no need to be angry just because he didn't do it the way you would have.