Yeah, if it *had* been posted to the board. But, see, I started playing around with the editor, and with tilesets, during a phase - lasting several months - when I was nearly completely offline, so I pulled tilesets from the tilesets folders of various levels I had on my laptop to play around with. None of this was ever intended for posting, and it didn't result in anything approaching a proper level, so I figured that it didn't matter if a few of the tilesets I used in my private playing around weren't public (there was no way for me to check, as I was lacking online access).
When I started building a 'serious' first level for publication - Falling Water, described on the previews board - I weeded out (or so I thought) all tilesets from my 'library' that I didn't find in the 'public tilesets' threads/pages. However, I seem to have overlooked a couple by Sinix, probably because my brain stupidly extended the public status of the forest one to the rest of them. Now, what with Sinix's statements in the forest tileset thread, it seems likely s/he'd be fine with me using the other one as well, but I'd like to make sure.