Poor dog. Maybe they'll be back and you'll be able to help him the next time.
It reminds me of the time I saw a young couple walking a very young puppy in Petsmart. I stopped the girl to tell her how cute he was and also mentioned they should carry him because he didn't have all his shots and could catch something. She was very nice but she told me she already knew that because her last puppy died of parvo! I tried again to convince her to pick him up but she was not having any of it. They wanted him to walk.
