The prior article was from a completely different source (IFLScience) and had different content other than one photo in common (from a quick glance). And I didn't see it, so I'm glad Diana posted this one, and that you back-linked the other one. Thanks to both.
Relax, take a deep breath, and thank God it's not radioactive.
(Unless you happen to be near Chernobyl)
It seems that the official explanation is “the coloration was likely industrial residue (such as copper sulfate or porta-potty dye)”.