Simon emails Blue, excited that it's snowing but upset about his day. He asks Blue if he ever gets so angry he cries, or feels guilty for being angry. Blue suggests that Simon eat Oreos to make himself feel better, and admits that he thinks he knows who Simon is and why he's angry. Simon replies that he thinks he knows who Blue is too, and sends a list of things he thinks are true about Blue, including that he has blue eyes, shares a name with a president, and once pushed him in a rolling chair. He also mentions the creeksecrets post. When Blue writes back, he says that most of Simon's guesses were wrong; he's not who Simon thought he was, and he hasn't been on creeksecrets since August. To ask Simon who he is, he writes "Jacques a dit" (meaning "Simon says" in French).
Simon's guesses as to Blue's identity (that Blue is Cal) show that Simon isn't exempt from making assumptions about other people, as at the very least, he's assumed that the only other person at school he suspects of being gay is Cal. Blue's suggestion that he knows why Simon is angry indicates that Blue is actually part of Simon's extended social circle and probably heard about or witnessed some of the bullying that happened.