It appears WWE officials were legitimately concerned with Mickie James, and instructed the referee to end the match early.
PWInsider.com has been told by numerous sources that the decision was made to ring the bell out of concern that James might actually have been out on her feet due to the way she was selling the move.
Mickie James looked visibly surprised when the referee rung the bell. She is fine, and did not suffer any injury. The report indicates she was selling so well, it caused those in charge to call for the bell.