very sad story here:
www.bbc.co.uk/news/uk-england-wiltshire-22542876
I've had a scare like this, because being a townie at the time I didn't know the issue. It seems that cows (especially with calves) may attack if there is a dog around. The trick apparently is a) not to take the dog into the field with the cows and b) if the cows appear suddenly, to let the dog go. It will easily outrun the cows and you will be left alone.
so I had a near miss, and this poor man did not. Perhaps mentioning it here will stop it happening to someone else.