I think the gentleman was probably expecting the OP to remain in the left hand lane as he didnt indicate to carry on to the right hand lane there.
As a lot of people think carrying on the straight ahead means go where ever the left hand lane takes you.
Being ignorant of the fact that no indication would be required, even if that was a right or left hand filter.
As I've said before, the amount of people who dont know when to use, and not use their indicators is ******* staggering.