One thing I would say is - is it a 'mound'? As it's made up of lumps of chalk (i.e. lumps of rock) it's a huge cairn in my book, but that's just being picky I s'pose.

No, it's a very fair thought, if the soil and rubble had eroded away and left a skeleton of rocks it would never have been called a mound. It's a pseudo mound.