"Oh my god, a random stranger who I know for a fact has a male voice threatens me! Let´s randomly attack the nearest girl with the box cutter I brought to school for no reason!"
Also, the mangaka is clearly contradicting himself at this point: In earlier chapters, it was said that her mother "fell ill and died" some time after her father disappeared. But now it looks like both of them "disappeared" at the same time. Plus Hasebe said in chapter3 that he "didn´t immediately started to follow the rules", but in this chapter we saw that he was one of the first people to follow the rules. He even actively talked others into following the rules.
Either Hasebe is the culprit and was lying or the mangaka isn´t even attempting to tell a logical story.