If I remember the photo correctly, it did look like dried fixer to me. If you're going to try a similar photo for fun and education, I'm pretty sure you'll need to get the fixer fairly saturated with dissolved silver to give tonality. It'll definitely crystallize without silver, but I doubt you'll get the full effect.
I might just do it, just for the nostalgia of inhaling all those toxic fumes once again. But I guess I'll have to make a bunch of prints first to get the dissolved silver into the fixer.
Hmmm. I guess developing a bunch of unexposed
printing paper should leave more silver in the fixer than exposed
paper, since silver has to stay on the paper to make the image.