WOB conflict Footnote

[Quantus Most Ancient]

I came across a WOB that I have a question about:

 

Quote

 

zebobes

Since Allomancy is powered by burning metal, isn't Scadrial going to eventually start running out of metal?

Hmmm... is that why there's a space trilogy? They have to mine asteroids and other planets for their metal?

Brandon Sanderson

It could happen. However, it's not really a danger with the current population of Allomancers. There just aren't enough of them.

Footnote: This contradicts other exchanges where Brandon states that burned metals return to the planet.
17th Shard Forum Q&A (Sept. 28, 2012)

 

 

The footnote says that this WOB is contradicting another that said the burned metals return to the Planet.  Does anyone know which WOB that is referring to?  The closest I can find is THIS ONE that says the "Power" returns to the planet, which I thought was taking about the Investiture returning to the originating Shard the same way used Breaths or Stormlight are confirmed to do.  Is there another WOB that the footnote is referring to?  If not, is there still a contradiction given our current understanding of things (since this WOB is from 2012)?

[Pagerunner Prime]

The WoB in question was from a paraphrased report from Phoenix ComicCon 2013, and it does not appear to be in Arcanum: 

It should be added to the Phoenix ComicCon event (https://wob.coppermind.net/events/297-phoenix-comicon-2013/) and linked in the footnote for the 17S Q&A entry. Would you like to make those edits? There are several other reported WoBs in that thread which need to be added, as well.