Fairness between boys and girls?

My 7 year old son and my soon to be ex's 7 year old daughter (they are 3 weeks apart) both got a hold of spray paint and decided to spray paint bits and peices of an old truck in our yard, well, My boyfriend was out raged I ended up my 7 year old on the and put him to bed at 8:00pm for punishment, My step daughter got absolutly no punishment for her part and even got to stay the night with her cousin, my boyfriend said but she is just a little girl, Does anyone see anything wrong with this picture?