@Kagamimocchi to add to what @Faryshta said it's also worth noticing that some ghosts ask our MC "can you see me?" and they leave because she ignores them, so there is an intent of something.
Also in chapter 14, the two ghots that were with the god in chapter 11 "exocise" (for lack of a better word) the creature in the tunnel when it said "you can see me". That indicates that something was about to go down. But it's true that she has no evidence of the ghots harming anyone.
Up until now i loved all this mangaka has done and I like tha fact that we are getting actual plot, but I'm a bit scared about the direction it will take. I mean part of the magic of this manga is the mistery and worldbuilding.
I actually think that the ghost tell her to stop looking because that teacher is a bad news, and maybe the ghost doesn't want him to become wary of her... maybe, just maybe... dunno, i just want something little positive in Mieruko's life, she's really need the hug