I'm sure the authors of the paper know that the warpdrive violates causality.
It doesn't matter that you're warping space to move points A and B closer from your perspective. If an outside observer can see you at point A at time t, and at point B at distance d away at time <t+d, you have violated causality, and an observer moving at a suitable velocity will see you arrive at B before you left A. That is a basic, irrefutable fact of special relativity.
It doesn't matter that you're warping space to move points A and B closer from your perspective. If an outside observer can see you at point A at time t, and at point B at distance d away at time <t+d, you have violated causality, and an observer moving at a suitable velocity will see you arrive at B before you left A. That is a basic, irrefutable fact of special relativity.