Sundance thank you for being aware and compassionate about the concerns you have for the dog.
You have done the right thing and addressed your worries directly to the owner, hopefully they will take it onboard.
Please don't just let this fizzle along for any length of time if the owner does not provide the basic food, water, shelter and exercise after a few days I would, and have done, reported it to the relevant authorities.
Animal welfare comes first excuses a poor second.