Heh, I guess I could see why U.S. customs officers would assume that if they're let in, they obviously won't ever return to Thunder Bay
My years of crossing the border have taught me that if there's one thing they are wary of (barring actual terrorists), it's people who look like they might stay illegally or work in the U.S.
(Incidentally, I have had many opportunities over time to actually confirm that it's okay for us Canadians to go and "work in the U.S." as long as one isn't getting paid by another party. That's the standard they're enforcing.)