I don't think I've ever seen a student council abuse its power this casually before.
She likely figured out why the other girl was "acting panicked" and make a call there and then. Frankly I think other then observing and isolating, they usually don't harm him under "circumstances" as long as he "kept his head down" with the other girl, it was simply
Here she now "has an excuse" to order Hiroto be "discipline" (hence the "saying he's skipping class" remember they can't miam, Badly injure or kill him. He's his sister's prey after all. But as shown when Forehead-chan headbutt him in the early chapter's beating him up is a different story PROVIDED of course they have good reason for it, which Hiroto unknowningly gave them. She likely got TIRED of trying to scare the other girls off and decided a "more direct reminder/warning" to Hiroto is in order to go back to "being beneath notice" as note they got FURIOUS when he accidently ran into his sister in the first chapter like he was suppose to AVOID HER at all costs as just the sight of him pisses her off to the point she had to INTIMDATE AND REMIND HIM of what will happen after graduation, and was CONSIDERING just doing it SOONER before being convinced to STICK to it! I'm still confused other then as said, his father's allies bringing up a STINK if it happens before graduation. The way she says it feels like she's preparing for some "high end battle" despite the DIFFERENCES in strength like she "wants to give him a chance to fight back" when the time comes or something like that! Either way as said they were PISSED and let him know it for "upseting his sister with his presence as though he KNOWS better!"
I do see Hiroto standing a chance if this girl is a Close Range Type as shown with his fight with the girl he's talking to and her uncle before where he showcased his new ability. Though difference is the Guy while strong was a Mudane Human, he's dealing with a High Rank Ability user of his sister's "personal Harem" LOL. As they say, the girls on the SC are considered QUITE POWERFUL ability users, and it's clear they all LOATHE his existence and wish ANY excuse to personally "discipline him" (and not the FUN kind either LOL) while being in on "Hiroto WILL die upon graduation by his sister's hand!"
Hiroto has only gotten so far with little trouble because his sister isn't in the school, and the SC is VERY adament to assure she's unaware of his "acting off script" as far as she knows, he's "obeying her indimidation and keeping his head down and not causing trouble" It's likely the story would be OVER, well his PLANS anyway if she WAS aware as the way 4 Eyes put it, she would be SUPER PISSED OFF that the rest of them have to deal with if she caught wind he's in CONTACT with anyone. First Girl was concluded as a Bully and ignored, no way they factored she had a crush on him and even AFTER the Hijack was reversed, she STILL chose to side with him, now aware of the whole "kill him" part and well, they did it together, so in her mind "he's hers" as she's into "weaklings" which was WHY she targeted him in the first place for her bullying! And Second Girl was someone even THEY found strange associating with him. Though 4 Eyes comment on "trash being attracted to each other" I have to wonder.
Really curious on her (4 Eyes) "DEAL" with Hiroto as she always calls him Trash, and I doubt it's ONLY because of her "being Yan Yan" for his sister who hates him. That insult feels more like something more "direct" between them he likely isn't privy to and thinks she hates him because of her closeness to his sister
I mean the Closed Eye girl thought he PURPOSELY made conflict with a girl they wanted on their side because it would give him a MAJOR ADVANTAGE, but we know while he's THINKING about it, he's unaware of what THEY on the SC know. Plus we know he's only trying to AVERT his sister killing him after graduation. Doubt it ever occurred to him to CHALLENGE her, but it goes back to what I mentioned with 4 Eyes "VERY Personal" hatred towards him coming CLOSE to match his sister's hatred of him! They talk like he's some MASTER PLANNER who needs to be under 100% watch and isolation least he cause trouble they're aware of, but he isn't! And I put it on the Forums for the EARLIER chapters, but I have a Theory that he may have been HIJACKED and this is the CAUSE of all the HATRED and "Sister going to kill him" as he has no clue why things are so bad other then thinking she hates him because he has a "Shitty ability" thought the flashback of her blaming him for a death and him acting like it was some "new memory" adds more evidence. Don't think his method of Hijacking is the ONLY method and their AWARE of his powers to an extend. Hence isolating him and placing him AT THE LOWEST TIER to assure he falls under notice. Including "pre-intimidating" the Low Ranks into "Persona Non Grata" him
They likely don't know about the GHOSTS per say, but they know SOMETHING