Interesting, thanks for the replies everyone. Yeah over the last 15 or so border crossings this year, I typically just get asked if I am declaring anything after going through global entry and that is all (even previously at YYZ). I was just caught off guard when the CBP officer went through an entire interview with me after handing him my global entry receipt and wasn't sure what might have triggered it. Maybe it's because I didn't have my passport in hand this time and was a bit disheveled carrying lots of stuff. Who knows?