Dog sitting Riley King

So, Jonathan's co-worker David and his family were going out of town for the weekend, so we agreed to watch their dog, Riley ("ToTo dog"). David brought Riley over last night, and we have him through Sunday. So far...Riley is a really good dog...very content without needing much attention (low maintenance). This morning, Cael was laying on the floor (right in front of me) and Riley heard a car door outside, so Riley barked. I was telling Riley to stop barking that everything was ok...I look down at Cael...he has the hugest frown on his face, then breaks down into his "sad face" and begins to cry! I guess the barking scared him a little bit! Riley doesn't seem to mind Cael's crying, though!