Indeed dgreening, I understand the problem the same way as you do. If you need to know the exact weight of a regular coin, you need a supplementary weighing. I think also about a balance with two scales, that only tells you whether what is in the left scale is heavier or lighter than what is in the right scale.
Your answer is quite right and complete, Venay.Singh84. This deserves to be 'The best answer'.
With 5 statements that can be true or false there are 32 possibilities. Most combinations are contradictory, but 4 are acceptable and without contradiction. It are the four that you mentioned. Unfortunately for the riddle this means that any thirteen characters, whether in the clues or not, will do. In fact it means that there is no problem. The man trapped in the room does not have to figure out a password because any thirteen characters are good.