When coming around EVERY corner that is 'blind' with NO prior knowledge of what can be around it, (no treeline or posts to indicate road layout) , no through hedge glimpses, no view or other roads about to join, no signs indicating a junction and road joining, in other words you have no concept as to just what maybe around the bend:
You should be travelling so that you can stop safely on your side of the road, (to use the FULL phrase here), in the distance that you can see to be clear in. If as you suggest that the car pulled out after you saw it with little vision of it's prior existence, could you have stopped 'properly' as above phrase suggests? No by your account.
So what went wrong, your entry speed to the bend was likely too high, giving you less time to assess the junction. Did you miss a sign or was it covered over ? (Tell the Council if it is.)
Let's say for a minute that you saw the car, and sped up believing it to be 'safe' well that can be an error. IF room, on the road layout I would have moved to the center, of the road, or even mostly to the opposite lane, giving the widest possible space between me and the possible 'leap out of junction car', as MUCH room as is safely possible to do so, given the unknown intentions of the waiting car. This allows for such a possibility and gives you extra space and so more control for this or any other sudden possibilities. Slowing a LOT and going past at a sedate, but steady rate, but not too much to look confusing and possibly, SO slow that they then think you are letting them go, needs to be judged at the time.
When looking at an unknown car's intentions: we can view the driver and look for eye contact and or the front wheels to look for movement. Never rely on passengers in your car or other cars.
By saying that you felt the need to gesture and comment, implies that you are not in control and enabled others to encroach into your space around you car, enough to give you fear and concern.
Good driving should enable you to have enough experience and ability to pre-control these possibilities, and make them always safe for you, as well as for the others who make the mistakes.
Whether you saw the L plate, should not really make *that* much difference, to what you could do here in this scenario.
Good driving often requires you, to use your ability to control your vehicle, and use your ability to risk manage & judgment to ensure that you do not get into these incidents, in the first place. If you do find yourself like this again, I would hope that your positioning and anticipation can help you be, in the right place, and out of any danger area when they occur, so the other person 'leaps out' but your anticipation has you in a safe place.
Then instead of gesturing and braking hard, you can smile to yourself, pat yourself on the back and either stop gently and let them out, or be away from any danger, and with a little throttle drive away distance yourself from their movements toward your car, and increase your space safety 'bubble'.
Think about it like this :
Never position your car into any 'CLOSING GAP' scenario.