What people often forget is that "in the wild" people don't just see a watch, but rather a complete image. So if they see the right person in the right environment with the right watch the thought of a fake never comes up. So I think in your friends case everything played well together. I think that's why vintage reps are the best to pull of (if they are done right).
After all they weren't that expensive when they came out and could have been passed along from one generation to another.
We also tend to forget that very few people (especially gen owners) look at a watch like the people on this forum do. They don't think about finding tells or differences, because they bought the real article and the question doesn't come to mind while all we do is to try to correct the smallest flaw.
I bought a MBK GWSD last month in Bangkok and wore it right away without doing anything to except to remove the horrible pearl. On my way back I stopped in Miami and went to the jewelry district looking for a pearl or a complete insert. I got offers to buy the watch from people working in two of the stores (for a watch that everybody here would have spotted in a second). Why? Because the watch was presented in the right context (guy over 40 in the right attire). And forget ADs, most people working there know basically nothing about watches, especially old ones.
I always tell my friends when it's a rep and other people have never questioned me.