I think this was expected? He probably won't get in practice until the end of training camp, but this lets them hold the roster spot for another arm while he rehabs. Doesn't matter until he starts the season on Reserve/PUP. We've seen the Patriots put guys on PUP before and then they come off in the first or second day of camp.
In other words, since you can take him off PUP at any time up to Week 1, there's really nothing to lose from putting him on PUP if he isn't going to practice, and a roster spot to gain. Do people in this thread think Branch and Hightower won't play all season, too?