According to popular Youtuber, Adam22, trusted sources have informed him that the shooting happened after Megan "violated [Tory's] ass" when he was giving Kylie Jenner too much attention at a house party.
"What I'm hearing, my version that I've heard from trusted sources is that Megan and Tory have been fucking. They've been chilling. They go to this house party. Kylie Jenner is there. I heard, depending on who you want to ask, that either Tory was showing too much attention to Kylie Jenner or Kylie Jenner was showing too much attention to Tory. Either way, Meg did not appreciate it. Meg-- maybe at this point in her career, has a little bit of an ego, she's feeling herself and she feels she doesn't have to deal with any disrespect. Meg was violating his ass. They got into a fight that was, like, bad. I heard that she was really shitting on him. It was bad."
Of course, this story has not been confirmed by Megan or Tory. Both parties have not spoken much about what happened. Adam22 says that after the fight, Tory fired shots when Megan tried to leave.