The way I understand it, Flashback and this person had intimate relations (but not a relationship), and they are both young. This person then had intercourse, and told Flashback to not to ejaculate whilst inside, but he did anyway.
my take is:
There is absolutely no way to know if this was an accident or malicious. As the intercourse was consensual, the absence of a condom was too (No evidence to suggest otherwise). Therefore this was a possibility all along, and they should've known it. To me this just seems like a story wildly blown out of proportion, two adolescents who messed up.
side note: The reason why I'm not hesitant to mention Flashback by name is because all evidence, including replies from the alleged 'victim' strongly point towards him being the alleged 'attacker'.