The Celtics also offered the qualifying offer to Rozier, so this could just be their way of doing what they have to to keep every option open. If the Kemba news is true, it looks like the Celtics would need to renounce Rozier, at some point, but could still be able to keep Theis' cap hit while signing Kemba.
Smart move. I don't think this signals some guarantee Theis is a Celtic next year, but it keeps the possibility fluid, at any rate.