tldr; if u have the "iron filings" u can progress the quest, don't worry about whether it is checked off in your log
They are the same thing. even if it doesnt check it off in the quest log, it is completed. this has been fixed in subsequent versions. The name "iron filings" means a similar thing as "powdered iron" but it has caused a lot of confusion for many people, and many non-english speakers have no idea what "iron filings" are, so ultimately I just changed it to "powdered iron" and removed all mentions of "iron filings" which is an improvement. However, this older version still has the "iron filings" name.