Thais put hazard lights on because they think it means GO STRAIGHT.
At a roundabout the car coming onto the circle will assume priority, so everyone copies.
Drive on pavements, up hard shoulders, the list goes on and on.
Could it be that they don't use their horns because they don't know how to?
Noise reduction here is non existent. Neighbours, dogs, music, talking in public....can't see why they'd take offence in a car, especially when they usually know what they're up to.
Possibly the fight/flight reaction from the shock.