IMO, this article is written weirdly, so have the main quote:

    During an interview with CTV News, Canadian immigration law specialist Warren Creates said:
    
    “The adjudication at the border is a lot more thorough, a lot more detailed, and perhaps at times a lot more hostile. It’s (...) because there are fewer travelers. Which means these same officers have more time to spend on each examination, that is to say, each person presenting in front of them.”

Personally, I don't know if that's the case: If CBP are told to be more thorough, then I'd expect them to be more thorough, regardless of how that affects the number of vehicles processed per unit time.