I'm not sure why pulling another child's pants down would be less offensive if it was a boy instead of a girl? The boy is 5 not 3 or 1, he should have known that was absolutely inappropriate behaviour.
OP, you seem to be really minimising his behaviour here. If another child had deliberately punched your son in the face because they were egged on and your child was upset, what punishment would you expect the other child to get? A wagged finger and clap on the back as they head back out to play?
I'm really surprised that there are lots of posters saying that going on the black cloud is really harsh, what do you think it's to be used for, murder? He behaved awfully, of course there was a consequence. That's the whole point of the traffic light/rainbow+cloud system.
The picture thing is probably just your PFB not knowing yet that not all pictures are treasured by the recipient and being sharp enough (at 5) to notice where it ended up. The teacher probably gets 50+ pictures a day, she will be nice and smile and say thankyou for all of them but no one has a fridge big enough for all of them to be displayed!
I would also be really concerned that my child was behaving like this so early on, two weeks on and already being deliberately physically violent to other children is quite shocking. If you can tone down your PFB tendencies I would ask to speak to the teacher to discuss - if you are still concerned about PFBs doodle not being treasured forever vs physically humiliating another child then I would just leave it (sorry if this is harsh advice, but if you can't see that you will be "that" parent for the next 7 years)