What I understand from the question is they're asking us what is $x = 3$ called, to which I'm answering a saddle point / critical point / stationary point. But $x=3$ is also a local minimum for the function when we double differentiate and put the value.
What would be the appropriate answer to this question? Where am I going wrong with the understanding? Please help
Basically you are on correct track. It is a critical point associated with a minimum at $X=3$, but not an inflexion or saddle point, as can be checked employing its second derivative.