Does this mean that there is no "proof of export" required for a temporary import in Canada?
Correct. For temporary import in Canada , proof of export from USA is not required.
That is to say that I wouldn't need to declare my car on the US side before crossing the border?
I did not declare my car on USA side.
Also CBP allows using exemption 30.37(q) if the vehicle is going to be out of US for less than a year. But since you were out for more than a year and weren't questioned upon return, I assume they didn't have a way to track the duration?
No sure about this one.