It has left me a bit confused because at some places the angular momentum/torques are taken about a point, while in others, it's taken about an axis.
Consider the 2 situations:
Situation-1: In a conical pendulum rotating with constant $\omega$, taking the angular momentum about the point from where it has been attached to the roof, yields that the magnitude of the angular momentum is constant, but direction keeps changing.
Situation-2: Here forces were acting on the endpoints of the rectangle and for it to be in equilibrium, Torque was balanced about the diagonal. (The solution specifically mentioned balancing the torque about the diagonal as axis)[The question was about the suspension of cars when one of the tires is raised a bit higher on the pavement.]