How did the driver know that you weren’t slowing down to stop on the left just after the junction?
The driver assumed that you gave them priority, they were wrong.
You anticipated the vehicle at the junction might pullout in front as you had not maintained eye contact with the driver so you checked the mirrors, altered your position to left of centre (extra safety margin), covered the brake pedal and signalled to any following traffic with your brake lights that you may slow down, you continued looking and assessing what the driver might do and at the same time you considered sounding the horn, as soon as the vehicle started to move you sounded the horn and performed an emergency stop.
You anticipated the vehicle pulling out, you was right it pulled out.
If the report form looks something like this then you couldn’t possibly be to blame.
The other vehicle tuck priority when it wasn’t safe to do so, the driver should have waited for you to stop before emerging if they thought you were giving priority to them.
In future when confronted with the same sort of situations try to take in all the information, look at the driver if he’s not looking at you he won’t know your there. Check the mirrors and gently glide out to just left of centre if safe to do so, it should be just a slight deviation in your normal driving position then cover the brakes, if the driver as not looked your way before you are within your actual braking distance you should give a couple of short notes of the horn to alert him of your presence then smile and thank the driver.
Any change in position and speed should be such that it is hardly noticeable by others including passengers.
My guess is that you over did the slowing down phase and mislead the other driver. Remember speed is a good indication of a drivers intentions, you could be slowing to give way or turn off but either way the other driver should have waited.
I think you might be reading advanced driving techniques such as IAM without fully understanding the concepts of what they mean.
Take care
Paul