I was wondering that myself. This was the first, and only, time they had been to the gravesite.
I read once that a dog’s sense of smell is 10,000 to 100,000 more sensitive than a humans, and even more in some breeds.
We have a doodle that is an epilepsy service dog for my son. She could smell an on oncoming seizure from the other end of the house, through closed doors and would alert everyone. They trained her with a sample scent from someone who just had a seizure. People donate the swabs in closed tubes for the trainers to use