Yeah, that really makes me boggle. It's one of my most matte inks. I even tried it in my Omas 360 Magnum which lays down such a concentrated/wet line it's a sheen monster, on Tomoe River paper and not a hint of it. I wonder if they had some kind of overstock situation and wanted to try and push some of it off of the shelves with dubious claims of sheen.
They might have mistaken the darker edge as sheen.