Do you have to be a US citizen to drive in the US?

I was told at the usa border: - an American citizen, living abroad, can own a usa registered vehicle. - you must have a 'tie' to the usa (this is the tricky part, many situations can be seen as a tie) in order to own a usa registered car and NOT be a resident. I was told this by the border agent last summer. I am Canadian, live in Mexico, and have a USA registered vehicle... got into a long discussion about it, the agent said I had to EXPORT the vehicle out of the usa since I have no ties to the usa ... he did let me through, as a favour (he said) since I was driving back to Mexico from Canada ... I would like a DEFINITIVE answer to this question though: WHAT IS A TIE TO THE USA?