That could be. Could also have been after the 2 previous outings where he handled it well, he said he would be fine again. He showed he could do it before. This time he couldn't so they decided to IL him.
Injuries and pain aren't a dichotomy, injured or not, in most cases. Most pitchers have some sort of pain after a month if they're lucky. It's a constant battle of what can they deal with and still perform and what needs time off.