My son feels guilty about his friend getting arrested

Hey guys... Another update with my poor babies situation. The gist of my other post, my sons friends found out my son is transgender when his period randomly came back at a sleepover. His friend's mom was so sweet and her son came by the house to play Xbox with my son and didn't mention ANYTHING about the period. The rest of his friends had questions but seemed to be cool with with it. My son went back there to spend the night and woke up to one of his friends hands down his boxers and fingering him. He came home crying. His friend(not the one who sexually assaulted him) messaged him asking why he left and his mom asked was my son okay.

Well my son ended up opening up to his friend today about what happened... And I got a call from his mom 2 hours ago that her son got arrested. He went and beat the shit out of the guy who sexually assaulted my son and is now facing an assault charge. His mom came over 30 minutes ago to talk to my son and explain it wasn't his fault and her son made his own choice and she's so sorry about what happened in her home. She just left and my boy still seems to feel guilty and said none of this would have happened if I could just be a real man. That broke my heart. He's in so much pain... Bright side... He's agreed to go to the police office in the morning to report it. He's hoping it will help his friend with the assault charge...

Edit: The friends mom is the mom of the good one. By her son made his own decisions she meant beating that gut up was her son's choice and its not his fault he got arrested and by she's sorry that went on in her house she's sorry she let someone like that spend the night.