There is always the chance something could have been lost in translation, but it could also be a case of recognizing that he makes a lot of money, and the Sox have both Vaughn and Sheets in the wings.
It would also be a recognition of he will be 36 by the time the next season starts, and it is getting harder and harder at this age to stay ready for baseball. It's a grind. Maybe he wants to relax a bit.
To tack on to this...
Pre June 21
3.98 ERA, 4.44 FIP, .263 BAA, .287 BABIP, 62% strike percentage 26BB/49K/9HR in 81.1 IP
Post June 21
6.58 ERA, 6.02 FIP, .316 BAA, .327 BABIP, 60% strike percentage, 33BB/46k/16HR/ in 80 IP
I have a bit of curiosity with him. His numbers tanked hard after the sticky stuff investigations started. One thing I am curious about was the talk about either stickier ball or a preapproved tack to be able to used for pitchers, and if that could get him back to where he had been, or if the losses are permanent.