I walked into that guy claiming everything that exists is natural no matter what and took the other side, because, well, it's simply not true. His stance is a lot like those who think you can't ever know anything, or that only what you can see exists, and the other fun, but useless philosophical arguments. It's a nice theory to talk about and have fun with, but it's just not reality. He was arguing that it was reality and I'm arguing against that position. In our reality, natural exists, and unnatural exists.
For thread purposes, cold forged iron is iron worked at low/room temperature and since it's worked iron, it's not natural. Hot forged iron is also not natural, but that does't work on the fey, because mythology.