You got it right! He's lonely!! Would you like being confined to a little kennel -by yourself- all day long? Dogs are pack animals and want to be with their family. Is there a good reason why he can't come in the house? It just sounds like he's bored and needs some good exercise and mental stimulation daily.

I don't mean to be rude, but I've never understood the point in having (or getting) a dog if it's just stuck out in the yard all day.