"Why not both" meme probably fits best. He has had some pretty bad injuries over the years, the one he got in the playoffs in 2017, we thought maybe he had a ruptured achilles in last year with the Preds, but it turned out not to have been ruptured. Anyway, I don't doubt stuff has taken a toll and he is physically diminished. He claims his hip injury is too bad to play (conveniently diagnosed after being sent to the minors by Philly, despite that he could play through it with Colorado). Philly apparently accepted that. At the time in letting him not report to the AHL, later in not pursuing a buyout, and right up until he started doing dance moves at his wedding? They were ok with LTIRing him and accepting his injured status. But at the same time, spotting grounds for material breach and termination was a bonus opportunity for them to save that LTIR hassle (plus whatever leftover amount insurance wasn't covering?)
He's probably "hurting". Which lots of veteran players are. To what extent he could play through it (in his case probably very ineffectively), vs. sit out on LTIR, I don't know. But according to him and his agent he needs surgery, they have consulted on that with Philly staff and third party doctors, and he actually had hip surgery scheduled at the time of termination. So I think it's fair to believe there is indeed an injury.