The multiplicity of a factor of a polynomial is the number of times the factor divides the polynomial. For example, in the polynomial $(x-3)^2(x^2-3)$, the factor $x-3$ has multiplicity $2$ and the factor $x^2-3$ has multiplicity $1$. In your example, the multiplicity of $x^3-2$ is _not_ $3$ because you're not cubing the entire factor: it _would_ be $3$ if you had $(x-2)^3$ instead.