The article is wrong in stating the police can knock on your door and require a breathalizer.
I'm not familiar with the details of the case: police both lie and fail to comprehend the law themselves all the time, so it's quite possible it happened as described. but unless they saw you get out of the car, they can't demand a breathalyser for exactly this reason.
See
https://www.parl.ca/DocumentViewer/en/42-1/bill/C-46/royal-assent
The two hour number is basically just setting time lines for alcohol levels. But the bill specifically address this situation:
(5) No person commits an offence under paragraph (1)**(b) if
(a) they consumed alcohol after ceasing to operate the conveyance;
(b) after ceasing to operate the conveyance, they had no reasonable expectation that they would be required to provide a sample of breath or blood; and
(c) their alcohol consumption is consistent with their blood alcohol concentration as determined in accordance with subsection 320.**31(1) or (2) and with their having had, at the time when they were operating the conveyance, a blood alcohol concentration that was less than 80 mg of alcohol in 100 mL of blood.