Glad you are OK Bob. 
I normally give a 2 second-ish headlamp flash when I am in a position to actually overtake past the slower vehicles, particularly so that the headlamp shows in the drivers door mirror. That way there is no reason why they did not see me coming and they cannot confuse the headlamp signal with an invitation to pull out.
Fair chance the other driver got as big or bigger fright than yourself, hence the tailgating/horn/headlamp thing......
I reckon more than half of drivers dont know what different sequences of flashing beams means, especially since these days driving instructors only want to tell you they're there to warn others of your presence, so as not to encourage people to use them as invitation to manoever
To clarify what I meant by a 2 secondish headlamp flash, its the pulling back of the indicator stalk to illuminate the main beams for a constant 2 seconds or so, not to be confused with a demented flashing like a morse code student on quadruple overtime......
Ultimately, the use of headlamps and horn mean only one thing - I am here..... Your descision as to whether headlamps or horn in what place. Personally, I think headlamp is the better option is the scenario described but each to their own...

Markie - yes, training coming to the fore again!!
