This is almost correct.
Anyway, these sprites are great, though they seem to be intended for a "Free Hexen" project instead. The trees, the shrooms, the tankards, the chains, the many keys, the gargoyle statue variants...
The story behind these is that several years ago, I set out to make a Hexen mod on GZDoom, codenamed "Black Metal Hexen" that had the two goals of A) "fixing" things that annoyed me about the original game, and B) Integrating a greater amount of gory/demonic/macabre elements as in Doom/Quake hells and black metal music/album art (hence the working title).
After a bit of playing around, I realized that what I was doing was going to require a lot of work just to have something that worked only on a proprietary game that I doubt many people play/care about any more. This was also well before the engine was even GPL'ed.
So, I decided that if I was going to have to learn/do all that stuff, I might as well go the extra mile and make a stand-alone like Freedoom, so I moved to doing a Doom TC (the engine of choice was always changing, at its peak I had some semi-working stuff laid out in EDGE, where you could walk around a partial map and kill some semi-animated monsters with a hatchet or blunderbuss. The DDF stuff and the map got nuked somewhere along the way though.)
After a time, I realized the horror and tedium of having to hand-pixel ~50+ sprite frames for every complete monster I wanted in game, and this was what stopped the project dead more than anything else. This was before I had any clue how to use 3D modeling programs to help cut some of the work, but even with it, monster spritework (and to some degree weapons spritework) remains the biggest problem (FreeDoom itself is testament to this.) So the project stagnated, but I kept all the stuff for it around, occasionally putting together a few more textures in case I ever took off with it again. When some similar projects came along, I just decided it would be better to offer up some of the stuff I'd made for use than let it languish in obscurity, since they'd been meant to be Free resources from the start anyway.
So, the stuff I made was always meant to have a Hexen vibe to it, more so than Heretic (although that had influence on some of the magic weapon designs), but it wasn't really designed as a 1:1 replacement, only having a similar mood to it. Places where stuff seems to match well are most likely the places where I said, "that thing was cool, and I want something similar."