Let's turn the situation around. Suppose it had been you turning right and coming up fast on a much slower cyclist. Then suppose that just as you were about to pass he moved across to the thru lane, causing you to brake to avoid hitting him. And suppose he had done this without signalling his lane change.
He was not about to pass me on the left. He was very clearly directly behind me... doing as he should. If there was any indication he was about to pass me on my left, I would not have moved left. It was quite clear he was going to wait it out, but he was obviously frustrated no less.