Hey guys, I thought I would chime in on this. I have had this happen before on occasion with water damage coming from the ceiling - my company has a flood division as well. Sometimes from the ceiling water gets around pipes etc. Long story short the water draining in the carpet could have rust residual. I have had to use rust remover on occasions to remove.
Not saying that this is the case but could be possible.
Not saying that this is the case but could be possible.