I don't think it was rigged. Although Hector was wise enough to use his reach advantage early in the rounds, he was quite open for Tank's hard punches. It didn't look good. It was just a matter of time before Tank would land a punch that would really hurt him so much. Tank could actually knock you out not just in early rounds but also in later rounds.
It was a good win for Davis because he will be fully confident to fight Garcia in April without worrying about any injury whatsoever. That would be a candidate for a fight of the year award if they don't really just consider running in the ring throughout the rounds because they are superpower puncher and has been knocking out their opponent lately. Unquestionably that one of them will go down and will never gonna recover after taking some power punches from his opponent.