I see dead bodies turning into that weird green skin on your duku vid. Is that from a tweak of some kind or something? It seems weird to load a tweak file just to record a demo. I forget how it worked, but there was a brightskin cheat that used to turn people into that skin- When you play back really old school demos, sometimes you see players appear to be using that skin, I'm guessing because the person who made the demo had the brightskin thing on somehow. But tweak commands shouldn't play back on demos, so I'm not sure what that skin is exactly.
Not accusing you of anything ofc, just trying to solve the mystery of the weird green skin. Is it a tweak? A demo glitch? Something else?
Edit: A picture of the skin in question, from a really oldschool demo I have from ocr^flocutus (pro UT player back in 2001). Note that I didn't have to d/l any custom packages to play back this demo: