I can so relate to this. Sadly I don't think we are ever going to get the chance this lady had.

I think many dogs behave differently when out walking with a big group than when being walked normally on their own or with not many others.

Big groups of dogs can make an aggressive dog 'shut down' as they are overwhelmed by the number of dogs in their vicinity.

My GSD is not dog aggressive so to speak but I know that if I meet another dog on a normal walk I have to be very vigilant of her body language and behaviour, but if I walk with friends or in a big group I don't have to worry at all as I know she will behave impeccably because of the number of dogs there.

So although this incident you witnessed was great for the dog i don't think it can be assumed that all this dog needed was to be trusted more and given more freedom as that could well backfire on the dogs 'normal' day to day walks.

I often wonder what Rupert would have been like off leash with strange dogs. Bit of a moot point though as Rupert off leash usually meant Rupert disappearing over the horizon in search or pursuit of prey. So even if he were fine with other dogs off leash he couldn't have been off leash anyway.

He was also very unpredictable. He could appear to be fine with a dog but the moment your full attention wasn't on him he'd go in for the attack with absolutely no provocation except for the fact the dog was there.

I totally agree with this. When Zena meets up with her little group of gsd's (5 or 6 of them sometimes), she's totally different. She was stopped from playing with her favourite once, by the Alpha of the pack who came over to her and had a go at her, she didn't retaliate, she went totally submissive to it and moved away from her playmate, whereas if that had been one dog on it's OWN, she would have most certainly fought her corner. No dog's gonna pick a fight in the middle of a great big pack of dogs who all probably know each other imo, unless they're stupid. Then again, I remember another time we met up, where the aggressive one which is always kept onlead had a pop at Zena, and she shouted back at it, and I went to stop her, but the owner of the other 5 told me she was right to do that, and once she had told this particular dog off like that, he would accept that she was above him and all would be fine in the future. It took 3 episodes of this before that dog accepted that Zena was above him in the rankings, and now he's actually friendly with her, he would never ever bark or snap at her now, we've even walked together on our own just the two of them and all was well. What did amaze me at that time was the fact that on the day Zena did have her last shout at this particular dog, NONE of the others took a blind bit of notice, whereas because they were a pack in themselves, I would have thought they would have turned on her They totally ignored it all and left her to it.

Zena is always, always pefectly behaved in a group of dogs out on a walk, whereas with a one to one with an aggressor I couldn't trust her 100% not to defend herself and not back down, she would never back down unless on a lead, I can control it all then, she's happy to shut up and keep quiet, gets pulled behind me whilst I deal with the other dog, it works for us.

So many assumptions
The big pack of dogs was 3 bitches who were at a distance - and two neutered males - both youngsters, one big, one small - politely wandering past.
The Doberman displayed no signs beyond friendly interest. He was inviting the youngsters to come closer.
The only aggressive one was the owner.

No, of course, I agree with you. The owner fully undestood that her dog was not 'cured' by any stretch of the imagination. She just relished the experience that on this occasion her dog was in fact enjoying the company of other dogs. I think the point I was trying to make was that she would have never allowed her dog of leash in this situation, had it not been for the guidance of others.

In the womans defence though, if you go on some dobermann forums, especially the American ones, there are lots of threads about male on male aggression. They drill into you that male dobermanns do not get on with other male dogs, even if neutered. A lot of breeders won't sell a male puppy to a home that has a male dog of any breed. Opie does get on with male dogs (just not his brother ) but I am always extra careful when he meets them for the first time. Even though I had benji to stay for a few days, I would never have another male full time with him. It's not worth the risk.

It could be argued that you made an assumption about this dog because of a couple of minutes spent with him

The point I was making is that you cannot possibly assess a dogs behaviour after a chance few minute meeting with him, yes his owner may have seemed to over react but you do not know his history... For all you know he could have a history of serious dog aggression, if he had been off lead and then attacked one of yours I'm sure this thread would be totally different!

I agree that a DA dog can behave very differently in a group of dogs, however, I disagree that it is because the dog has 'shut down.'. (unless the dog is leashed and forced into the group).

They are less likely to single out a dog and are more careful to not cause trouble but it can work wonders for a dog that needs to improve their social skills and confidence. However, that is not to say that it is suitable for all dogs and the group really needs to be a group of stable, reasonably confident dogs.