Yes the dude turned without a signal but I have myself avoided disaster many times by calling out to cyclists I thought may be getting ready to turn in front of me. The dude with the recorder seems to be deep in conversation with his ride partner. Really should have paying more attention to his surroundings.
A "heads up" or "passing on your left" will do the trick.
In all honesty, I think both riders are at fault in the video. Pretty slow speed crash but I myself at any speed, especially higher speeds will alert any and all cyclists ahead of me that seem to be a bit suspicious.
The guy had no clue, give him one!
