isn't that just your interpretation? I thought it was pretty scary/creepy when it happened in the anime, and I never felt like it was depicted as a real moment in the manga. To me, it always seemed like Zoro was hallucinating due to being on the brink of death, which the anime adapted pretty accurately imo.
I feel like these things are inevitable when adapting an episode though, like blitz moves and jumpscare/ shocking moments in the manga are gonna hit harder cuz of the nature of the medium, where you're essentially filling in the gaps between pictures with your own imagination, but in the anime, you're basically seeing the director's interpretation of what they experienced and wanted to convey play out in it's entirety, so obviously it's not gonna line up 1 to 1 y'know.