He's talking about how elemental iron on earth binds to oxygen and that carbon monoxide could be used to reduce this but I have no clue wether martian metals are oxydised or not.
We think Mars had plenty of oxygen in the past, but because it's a smaller planet the molten core solidified. Without molten core no magnetic field, and without magnetic field most of the atmosphere was stripped away due to solar radiation, leaving only some heavy CO2 behind.
With that in mind, any metal ores had plenty of time to oxidize just like on earth. But metal from asteroids that impacted over the last two billion years or so should be unoxidized.
