moondae was already being bullied before that, everyone thought he was weird. bullies don't really need or care for a 'valid reason' to bully others. though i think it would've made more sense if the rumour was that he stole a used pad because that's pretty gross and weird.
girl, i want to bitch slap his mom so bad. until the end that bitch just keep gaslighting him that everything she did was for his own good.