Nope nope nope, OP. Fuck his picture and your attitude.
If he is NT, then 5 is old enough to know that other people's bodies are off limits, that underwear is private, and that he was doing something wrong.
If he doesn't understand that, then all the more bloody reason for him to be punished and educated now, not to have his mother minimise his nasty, bullying behaviour by fretting about his confidence and blaming another boy/the teacher/ whoever.
Today's 5 year old humiliating a girl without consequence in the playground is 2027's Brock Turner.
1/3 women are sexually assaulted in their lifetime. Atttitudes towards women are formed from nursery school.
'Boys will be boys'
'But What was she wearing?'
'It's not his fault, he was drunk'
'The other boy suggested it'
Obviously a 5 year old isn't a sex offender, but OP needs to educate her son and correct his behaviour now, not teach him that he is entitled to feel confident and good, even when he's just violated someone else's body.
If OP has left the thread, I hope it's to apologise to the girl's parents and to discipline her son.