If you study, they are easy. However, as you say, there are always space for luck although it sounds unlikely.
0.333 probability of getting an answer right and assuming independent questions despite there are 20 cases, the probability of passing the exam by pure chance is like (0.333)^(120 x 0.65). Note that 0.65 is the assumed MPS.
Of course, a 0 probability does not mean the event is impossible. The probability of people dying in a plane is zero, however thousands have died around the world so far.
The conclusion is that another factor or factors make that 0 probability to be in fact much higher. About the CFA exams, it means that people still know their stuff and allow them to pass; and saying that they are not that “bright” results in a mistake. Perhaps they show themselves as not bright or easy going, however they can get the things correct when it is demanded. I know people like that, perhaps I’m one of those people too. I would prefer not to judge, nor the CFA exams, nor the candidates.