it reminded me story of friend of friend who went to pakistan from UK, here its very common to wave hands in thanks while driving to other drivers on the road if someone stops and give way to you etc.
she was used to it and done the same thing in pakistan to a guy who was driving , and that guy took it as some kind of invitation and started follwing her car and ended up near her house. Then she realised what has she done, so she stopped and explained it to that guy! :)
this is cultural thing!, well builders here dont have good repute to say hi anyway, they will not let any girl pass by without passing any comments in england. I dont know why this girl done that.
but for bus drivers and etc, its cultural not to talk to them! if some one does they may take it in some other way cause its not normal in Pak.