Yes the curve has 2 inflection points, so if it were a polynomial is would have to be quartic. (Cubic polynomials have 1 inflection point at most). Buz I dont think this is a polynomial.

Yep you’re right, I said something daft. It looks pretty much like a Gaussian doesn’t it?

small tails. maybe. it could be anything though with the right parameters.

Definitely not a cubic function though, you can't get a polynomial to hit 0 that nicely. Any polynomial's leading order term will dominate as x increases. Unless they're using a super high order polynomial and hiding the blowup off the edge of the plot.