If you rely on official statements, Cambodia and Vietnam have a long tradition of friendship owing to the strong ties between their leaders and ruling parties. But an undercurrent of irritants such as constant border incidents, though minimal, suggests deep discontent or distrust on both sides.
It is worth remembering that before being labeled as China’s puppet, Cambodia used to be called Vietnam’s puppet.
It is normal for small states to be seen as puppets of stronger states that they have good relations with. “Puppet theory” is being used to humiliate small states and allege their weaknesses, lack of independence and sovereignty when their national interest does not fit with geopolitical agenda and interest of the theory’s proponents. It can be shaped through repetition of accusations.