[Soundy]

If nothing else, the poor thing is probably bored to tears. They probably put him outside so he won't destroy furniture, which I would bet he does out of boredom.

Why don't you offer to take the dog for a long walk or to the park or something, for some exercise? Don't accuse them of anything, cuz that will shut them right down... tell them a sob story of how he reminds you of your old dog you had to give up when you moved there from some eastern country and how you'd really love it if you could take him for a walk now and then, and how he might enjoy the exercise as well. Don't give any indication that you think they're shitty dog owners.