It didn't make much sense to me, and I assumed that they'd picked a middle-aged, grey-haired, white guy so that they couldn't be accused of racial profiling... but from comments here it seems it is a lot more general.
Some of the questions didn't make a lot of sense (especially not at gone midnight), one or two were personally rather insulting, and they seemed to think that I was over here for employment rather than business meetings.
Getting into China the following week, on the other hand, was a model of efficienty and politeness...
My most recent entry into .ca was quite the opposite. Bear in mind these are very rural crossing points, nothing like the I5 transit. The most recent Canadian agent was somewhat gruff and unpleasant, asking quite a few questions. Come to think of it, in a prior .ca entry, with a female friend from the UK, the Canadian agent seemed to be convinced that we were entering Canada for the purpose of getting married and asked us repeatedly whether we had such plans. After multiple denials, he went on to advise us not to do so anyway. What??? My crossings back into the U.S. from Canada very recently have been fairly painless compared to going the other way.
I've had nothing but good experiences crossing the border at the Thousand Islands Bridge or Massena, NY. Both ways, everybody was kind, friendly and patient. I hear nothing but horror stories about Niagara falls and the one time I flew into Vancouver was less than pleasant.
Just some more n=1 to stir the pot. :)
I've also been subjected to extensive physical searches of all my belongings. (And just to be clear, I'm a healthy, Caucasian, 20-something, US born-and-raised, male.)
I often think of most Canadians as being friendlier than a lot of people around the US, but immigration and border control aren't one of those areas.