I think they were just tired. Looked like they might have had a tough practice the day before and didn't have rest time to recover and Jags traveled so they had some rest time. If I were coaching I would have practiced the day before cause preseason games don't matter and getting in shape for the regular season does.
I coached High School football for 15 years and have seen my teams play flat like that before because I didn't rest them enough before a game. That's just my opinion from what I observed.