I re-read what I wrote and realize I only wrote half of what I was trying to say.

These dogs are not encouraged to be social and are never formally socialized towards other dogs. What's expected is that the dog will be neutral at reasonable distances and able to WORK. That is his sole function in life. They will put up with some jerk behavior from the dog(comes with the working personality) if it's a good one.

I guess what I'm trying to say is that the dog may be perfectly fine towards other dogs after he's actually socialized but at the moment he may need to be handled more cautiously around them. I certainly wouldn't let a MWD interact with another dog until I knew how good his social skills were.

Most of them don't seek to interact with other dogs anyway. They're happiest just being a team with their handler. Living with another dog is just not a skill he would probably have right now. At 8 years old they may have made the decision that he should just remain an only dog.

It's quite possible that this dog has never interacted with kids. That does NOT mean he is aggressive. They mention that he likes to play rough. Up till now, almost every person in this dog's life has been able and willing to play rough. Dogs don't automatically learn what a child is. He would have to be taught appropriate interaction with children. In the mean time he is probably a hazard to younger children.

Hopefully they can find a former handler or someone else who understands the life this dog has had. Working dogs don't live like pets and there are some skill sets he will be missing that might give the average pet owner problems. They should be aware of them but just calling it outright aggression would be wrong IMO.