How is Diaz's camp high? He makes an interesting claim about the weight, the drug test is another story.
Per the UFC website:
In non-championship fights, there shall be allowed a 1 pound weigh allowance. In championship fights, the participants must weigh no more than that permitted for the relevant weight division.
How does the UFC handle a champion not making weight for a title fight? This could fall under that category.
I saw the video of when Diaz was told about the weight, it seemed really odd and didn't make sense why he was told just before the weigh ins. That information would have been useful way before then.
Also, from the Quebec rules you linked to:
74. The organizer shall provide a scale having a minimum capacity of 200 kg (440 lbs). The scale shall have graduated readings at each 100 g (3.6 oz) and shall be certified by Measurement Canada.
The scale shall be electronic and of a model approved by the board. The organizer shall adjust the scale at the official weigh-in, in the presence of the person in charge of the sports event.
So, if 170.9 is the same as 170.0, what is the need for a scale that has decimal readings?