I've highlighted parts of the image I'm concerned with:

In other words, they want a cubic polynomial, i.e. $\displaystyle P_3$, and if they say that a given polynomial's degree is $\displaystyle n+1$, they must choose $\displaystyle n=2$ so that $\displaystyle n+1=3$.

Perhaps they should have written the degree of the poly is $\displaystyle n$, not $\displaystyle n+1$?

Something here seems inconsistent to me.