unexpected questions

Finished my schooling so I went back home. They asked to write my American address at the Canadian border, how long my program was, and all sorts of other questions. What is the purpose of all these questions? As I am a Canadian citizen, aren't these American concerns and not the home country's?

Thank you in advance!

They were probably making a determination whether you were Cdn resident or non-resident during your time away, likely to determine what duty/tariff code you fell under. Did you have lots of stuff with you?

There may also have been some info gathered for the US; after all you were handing them your I-94, which will be forwarded to DHS. Maybe they simply thought finishing school in late september was a tad unusual.

If you don't give them a B4 at the POE they're required to grill you.

Thanks for your responses. I traveled with just one large bag and nothing to follow and gave them an itemized list of what I had with me with the value of the stuff. Surprised the checked my suitcase, wallet, etc. Do they exchange information with the States about arrivals and stuff? Didn't realize that. Thank you!

Of course they exchange information.

Yes they do, it's SOP to question you if you don't present the right forms, i.e. CBSA forms B4 and B4A. They have to determine the answers to the questions on B4.