Could they have been digging as a possible "rescue" attempt? Perhaps not, the scent would probably tell them it wouldn't help. I've had cats work with me to find other lost cats, and I had one cat who was so upset when her adopted half-grown kitten-son was missing, she stole a hot dog off of the stove and went outside carring it like a cigar, yelling around it for him to come and get it. (He turned up later) So I don't find something like this to be beyond belief.