That's what that means, yes (in terms of DR)- the cold iron vs. fey is an occasionally-mentioned canon thing, inspired by european folklore. Generally fey are not terribly well developed in WotC canon, so bit and pieces of things elsewhere get worked in as well to fill in the gaps (Changeling kiths, etc). One source I was pointed at while doing research on them for a Northern Cormyr plot a while back was this:
http://www.wizards.com/default.asp?x=dnd/arch/fey
Which does reference cold iron, seelie and unseelie courts, and many other tidbits of fey lore. It's not FR-specific, so of course subject to the Greenwood Rule.
Granted of course, cold iron is a very specific subset of metal.
None of this particularly restricts DMs from inventing specific preferences or vulnerabilities with specific groups of fey though- which is what the situation that drew the initial inquiry reflected. The actual intent of the DM(s?) in question may well have been plot-related, but forgotten over time and change of personnel- happens all the time in places like ALFA. At some point these things become a part of the ALFA-canon, and add depth and interest to an area, even if they don't serve any clear or current plot purpose. They also stand to give opportunity for future explanation/development by creative and enterprising DMs.
I would generally agree that most fey would have no problem with most metal. Fey that have specific vulnerabilities to Cold Iron, may have a strong dislike for cold iron, since it's not the sort of thing that gets used for much besides overcoming said vulnerabilities.