I'd bet there's a 100% chance he got the shot in his non-throwing arm.
yes, but while the stiffness I think is commonly at the site of injection, isn't there sometimes a side effect of broader aches and soreness? If soreness is tied to inflammation, and you are doing something that ordinarily causes inflammation, then maybe . . .
Of course, they would have been dumb not to wait to today to give him a shot.