The officers were "dirty". They brought me in a room to do an interrogation where one officer asked questions and the other took notes on an old computer. I literally told them: "I am not going to stay past my return date" and the officer asking questions told the officer taking notes to not write that down. They asked who my parents were, how much money I had, my employment history, what I did in the US while working on my previous TN, if I was in danger, etc.. They asked if I was applying for jobs and I said yes because I was unemployed. They then asked if the jobs were in the US and I said I would accept another TN job if I could. They call the process a "sworn statement".
For those of you who go through that, don't agree to the statement if they modified it, like mine. There's no cameras or recording devices so they can be dirty, and they abuse that fact. You have no rights at all at the border, and your assumptions on decency and honesty are not correct.
My assumption to this day is that they thought I was trying to work illegally, but this is not the case.