Why in the tests is [11,13,29,31] not a good parallelogram but not [26,11,13,24] ? (the one drawn in picture is {11,13,26,24})

Both set of points don't form a proper geometric figure with points put in this order but can form a parallelogram when put in the right order.

And maybe you should add explicitly the condition if the points need to be in a particular order.