I definitely wasn't meaning to imply you were naive, and I apologize if it came off that way. 
I guess I can't say for sure that they don't have a flock of chickens at their house with one goose guarding them, although my guess would be that they don't. But I do have experience with keeping one goose alone, and then multiple geese, and I can tell you with 100% certainty that they are happier as a flock than they are alone with another species.
I also still do not believe that a lone goose is a better guardian, again, from experience. My geese seem no less alert now than when I had just one. Now, they just can spread the watching duties out and take turns keeping an eye on things. I certainly haven't started losing more birds to predators since getting more geese.
In a flock, they can take turns and share the duties looking out for danger - one will take a turn, keeping an eye out, while the others graze and relax, and then another will take a turn so the one that was watching gets a break and some time off too. A lone goose has to do it all on its own, without getting a break. And it would have to be trying to watch every direction at once. And it's going to be more nervous because it has no help if things go south. So it would appear more alert than all the individuals in a flock will.
Plus, just the presence of more geese is likely to deter a predator from attacking. Where a fox might not hesitate to go after a flock with one goose in it, the presence of a bunch of geese could make it think twice. A hawk isn't going to want to take on a bunch of geese for a chicken dinner, etc.
I've also see the argument that they won't protect the chickens as well if they're raised with other geese because they imprinted on other geese and not chickens and therefore don't consider the chickens part of the flock. Well, you could always just raise a pair of goslings with chicks if that's a concern. They imprint on all their siblings, so they would imprint on the chicks too.
They really are intensely social flock animals. Before I got more geese for Lacie, I guess you could say she wasn't unhappy. She had food, and water to swim in, and she wasn't alone. But she wasn't a chicken or a duck. The chickens and ducks preferred their own kind to her. She wasn't excluded, but she wasn't particularly included either.
I knew she wasn't as happy as she could be. So since I wanted her to have the best life possible, I fixed the situation and got more geese. Now she has a flock that she's very bonded to, a mate that protects her, and is even a mother. And she's much happier. For geese to have the best life possible, they must have other geese to be with.