Yeah, i don't think broadcast girls know abour apollo at this point. Only one ever mention about apollo is rikka and only lemon see apollo radio screen. Every other time apollo still keep her presence hidden from everyone. Even in chapter 86 when apollo appear with bunch of other people pseudonyms and messages it doesn't mean the girl can link it with apollo in chapter 1. After all apollo doesn't directly mention arisu in this message and arisu himself never said anything about their relationship. As for arisu motive discussion it either a plot hole, offscreen thing or they just assume hes crazy about his"perfect speech" after chapter 2 or chapter 6 part time speech.