No, inbound flights are subject to local boarding security personnel and regulations. That's why some countries can't fly to the U.S., because their regulations are so slipshod. I
Think Nigeria for instance is on that list, but I can't remember for sure. Next time you fly internationally, they have posters up warning folks about those countries.
The CBP screening, that's a pre-clearance thing, where we have officers in foreign ports to screen passengers before they arrive here. It's kind of a convinience thing, I guess. Get you processed before you're tired from an international flight. It's the same thing you go through when you arrive at an airport here.
Do you remember if the CBP guys on duty in Canada were screening for weapons, or just things like (CITES, Fruit, Meat) a rhino horn full of heroin and Khapra Beetles?
They xrayed the baggage and only wanted a look see when they saw my 3-4 bottles of wine. Plus they wanted to know what was in the tin cans - Cassoulet (a French, bean and duck dish) it was a week or two after the 7/7 England bombings they were thorough.