True, but the goal is remove the unintended cheating from shoulder-surf (or stream snipe) by watching everyone streaming the same game. As soon as someone dies, it does come back to "did you see who?" and the victim would already know who it was if they were watching carefully.
Especially from spectators to the stream. For the streamer, they can hide their twitch/youtube chat while they play so they're not tempted, but they can't keep people from watching multiple streams to sus out who the impostors are just by looking at the names on top of the characters or the voting screen. I was watching one set of twitch streams the other day, and it's like within a minute people in the other chat windows are already going "it's (other streamer)". So the idea here is to make sniping the stream unreliable.
Another way to accomplish the same thing, albeit requires a lot of effort on the part of the developer, would be to generate a "camera" and "microphone" output from the game and the streamer can then map their microphone through the game through discord or OBS or however way they want to stream it, and just send an alternate image/audio during the parts that would spoil the game. Like a greyscale mosaic over dead bodies. Creating a second copy of the game to run that just relays the info without the spoiler data is easier for streamers to understand IMO.
While I think the audio unintended cheating/self-spoiling is a problem, at least when you play with people you know, on twitch, that can be rectified by having someone controlling the mute buttons that's watching the stream but not participating.