We don’t know and it’s never been disclosed publicly.
However, since he was promoted to assistant head coach less than a year ago, it would appear unlikely that it was a one year deal. That’s just not typical.
Coordinator is not typically seen as a promotion over assistant head coach.
So, it’s unlikely he could leave for anything less than a HC position.
He could be named the Cowboys DC and still retain his Assistant Head Coach title. It would probably give him some more money and be an additional feather in his cap.
If he signed a one year deal, then he can do whatever he wants.