For one, he "felt great after" his bullpen session, which is much different from when he felt soreness last week in Toronto. Also, he threw all four pitches and not just fastballs. For a pitcher, once you're beginning to throw all pitches, it's another step in the comeback from an injury. And when it feels good to throw those different pitches, it's even better.
(April 13, 2017 - Source: Maddie Meyer/Getty Images North America)
Another note is that I really like players using twitter for this kind of stuff. It comes straight from the horse's mouth and much more direct than being translated through beat writers. From a performance standpoint, Price coming back will definitely help the Red Sox. Steven Wright is struggling and since he's a knuckleballer, it's unknown as to if or when he will find his mojo that he had last year. By bringing Price back, the Sox will have the option to give Wright some time to find himself.
Price will probably not be back for a little while, but he is at least on track to be back when the Red Sox proposed he would be back, which is mid-to-late May possibly early June.