I think he may be referring to rust inside the brake lines. I've seen it before on an older vehicle that probably never had its brake fluid changed. Over time, moisture gets into the system and corrodes the steel brake lines, causing rust to get into the fluid. It's why you have to change the fluid every so often: it's impossible to keep moisture out, and the fluid is hygroscopic.
Please stop getting involved in flamewars about brakes or otherwise. Tedious back and forths like https://news.ycombinator.com/item?id=19001513 are something we're trying to avoid here.
Please don't engage in nasty spats on HN. If you think someone's behaving abusively, let us know at hn@ycombinator.com, and avoid breaking the site guidelines yourself.
