Left Hand Drive

I was coming out of a filling station, waiting on a break in the traffic I notice a oncoming vehicle with the driver reading a map. I immediately sounded my horn big time as they the vehicle passed. It was at this point I realised it was a left hand drive car and all I could do was wave hello to the occupants ..... They look at me as if I wasn't wise .... they may have got that right ..... oops..