Answer
He got the opposite values of $C$.
Work Step by Step
The general equation for a circle with radius $r$ and centre $(h,k)$ is: $(x-h)^2+(y-k)^2=r^2$.
Hence here the equation $(x+3)^2+(y-2)^2=16\\(x-(-3))^2+(y-2)^2=4^2$
would suggest $C=(-3,2)$, $r=4$. He got the opposite values of $C$.
