I used forever black on my rear corner plastics a few months ago. It is definitely not textured, and it's not supposed to physically coat the surface like paints or other coatings. It's basically like a leather dye that is designed to penetrate the pores of the soft plastic and change it's color. It does sound like what you saw was in-fact spray on bedliner, as Jeff suggested.
That being said, I didn't have the greatest experience with the forever black, and I'm not really sure why. I read dozens upon dozens of reviews, and watched multiple YouTube videos about how to apply it correctly. As with any project like this, the preparation work is the key to a good result. I spent a full day cleaning my plastics - first with goof off, then with alcohol, then very thoroughly with soapy water, and finally with the cleaner product that came with the forever black. I wanted them to be 100% free of wax, armor all, or any other product that had been used on them previously.
I ended up having to apply several coats to eliminate streaking, but I chocked this up to my plastics being in pretty poor shape to begin with. Ultimately, I used a foam roller to get even coats that didn't streak (this was recommended in many of the reviews). They looked BEAUTIFUL for a while, but I've recently noticed that the product is now flaking off in spots. Clearly, it coated the surface rather than penetrating it. I'm not sure what I did wrong.
Here's what they looked like when I did them. In the first few photos, you can clearly see the steaks when I did the first couple of applications with the foam brush (before using the roller):
http://www.sccxterra.com/smf/index.php?topic=2455.msg48945#msg48945