OK, yesterday I was behind a slower cyclist, and another cyclist was behind me. I checked behind for a gap, called out "coming past on your right, mate" to the guy in front, and proceeded to overtake.
Next thing I know the one who was behind me came past me without a sound, so close that his left elbow made significant contact with my right arm. He could easily have made me come off.
Not an apology, he just blasts off. I tried to catch him, but he turned off at the next junction.
There was enough room for him to have given me more space, and if there wasn't, he should have waited until there was. Idiot.
Anyway, I'll look at the video to see if it's worth putting up. Rather annoying.
Yes, it is annoying and your sanguine response is creditworthy. It has happened to many of us in more than one mode of transport - and many of us have been the cause too....
It raises an interesting point about the issues arrising when three vehicles (bicycles or similar) converge in the same direction at three different speeds. All need to be accutely aware of the intentions and position of the others.
You gave a verbal indicator (a good thing and I rarely bother when on road) but did the chap behind hear you?
He won't have been listening out, but may have been watching for your hand or arm to give some indication. You may have indicated, but there is no mention of your having done so.
You knew he was there and that he was closing on you, but his pass on you seems to have surprised you (up to a point). This suggests that you may not have shoulder-checked just before pulling out. I'm not saying you didn't... I wasn't there.
These situations can assume Rashomon-like qualities, so in a sense it matters not whether you did.
But... As the three of you converged the rear cyclist will certainly have been thinking about who would pass whom first. You and Johnny Slowboat were both in his field of vision and he could see your relative rates of convergence. He may or may not have made a judgement.
If (very big if) he pulled out to pass you momentarily before you pulled out, he may feel aggrieved and you may have been experiencing a 'punishment pass'. Very wrong, but some would say mitigable. I would not; particularly the contact - which can be catastrophic).
Once you knew he was closing from your rear and once you'd decided to overtake Johnny Slowboat, both you and Carbo-Missile had a responsibility to check and respond to the speed, changes of direction and indications of the other.
It is a shitty thing and it is annoying, but this happens quite a lot in cars, on motorcycles and on bicycles. Mr Carbo-Missile sounds a wrong 'un, but the finger of rightful admonishment in these situations sometimes points slightly towards Johnny-in-the-Middle too.
I write the above with no knowledge of the situation beyond your words in the OP, but having seen similar things a billion times and using my own natural prejudices to come to the right conclusion.