I found the explanation of signal number 002 a little bit lacking. It should be something along the lines "Tell someone who isn't a classmate about what happened in the audiovisual room".
If there is ever an anime of this manga/LN, this chapter should be the first few minutes of episode 1 just to troll the audience into believing this is just another generic isekai story only to start with the actual chapter 1 after the OP or something.