Wow. If that's true, it's really dangerous! One of my biggest bugbears in the UK is people who don't indicate their intention to pull out or pull in to a different lane on dual carriageways and motorways. How on earth is anyone supposed to know that you plan to change lanes if you don't indicate?
It certainly appears that those drivers are trying to send a message to the indicating driver that he/she is using their turn signal inappropriately (in their opinion!) I assume that the other cars bunch up and fill up the space that the indicating car wanted to move into.
Student or Learner