To expand on why I'd draw a distinction between the Ghost and whoever's been cursed... the Spellcaster is a role I took directly from the card game, who removes their victim's ability to speak out loud for a day cycle. They can still communicate by gesturing though, which would include things like pointing to other players and nodding in agreement, so quoting posts to respond to feels within the spirit of that.
The Ghost was also originally pulled from the card game, but I've modified it from the last time I ran Werewolf, where the Ghost didn't have any extra information at all. In the card game the Ghost writes one letter per day on a piece of paper, and has no additional information. As our games go on for a long time though, I wanted to make the role more fun and active as a consolation prize for dying first, so I introduced the random information. A ghost is still a dead player though, and were this a physical game, they wouldn't be using body language to react/communicate, which is why I would rule against quoting posts to react to them.
I hope this makes sense! There's an internal logic I'm working from here but it's hard to communicate haha
