I would go with other, I think it was a combo of multiple things. I think his body was beat up after a huge amount of big hits and back to back deep playoff runs and a shorter offseason to recover. His head wasn't there mentally after his holdout and money issues (in his mind) and maybe there was some small issues with some teammates after his holdout cost them a chance to get off to a better start the first few weeks of the season. I would also say he might have just lost a step as he gets older, but with a healthy offseason and chance to heal up a bit I could see him coming back and having a good year to prove last year was just a off year.
Then again, I could see the team moving on from him if he wants to play the money and contract game again this offseason. The team really needs to have a quite and productive offseason (good draft, resign, restructure and sign some worth while RFA and FA, and just get some key parts healthy). I also think the coaches not leaving this offseason (i.e, Bradley and Quinn) will be big towards next season success with some players.