the boy since this occurred has stopped going to the babysitters..is it possible that he could have behaved like that only because he saw a dirty video or could something like that only happen if someone was actually molested? and if he wasnt molested and simply acting out something he saw will he still need counseling and will he ever forget what he saw or is he going to keep acting it out and why..kids see all sorts of images today including people killing people but they dont go killing people because they saw it on tv especially a child this young..
Sorry, when I made references to "your son," I meant your friend's son. I should have proof-read that before posting.
Your friend needs to have a talk with the babysitter first and let her know that because of her teenage boys viewing porn (which she may or may not know about) has been seen by your son. In that case, she will no longer need that babysitter's services because obviously she can't keep track of a 7 year old well enough to see that things don't happen to him that shouldn't. What if her teenage boys molested your son? That is also a possiblity, and your son is not telling you they did (to protect his abusers, which is common).
She needs to find a new babysitter for her son. Preferably one without other kids to watch, as now her son may "act out" on other children, and preferably not one with teenage boys. In fact, she should consider a public daycare where the supervision of children is constant, often with one to three teachers at all times for a small group of kids.
As for the boy, his behavior is not "weird" or "abnormal," but rather learned, as you suspect. Children act out what they are taught and what they see. Someone has taught your friend's son to do what he's doing, and your friend needs to address the source of that and take action from there. If he was molested, it's critical that she speak up for him NOW, while he is still young enough to respond well and quickly to help from a therapist. This will not reflect poorly on your friend as a mother. What WILL reflect poorly on her as a mother is if she continues to do nothing because of an irrational fear of him being taken away from her and his life getting turned upside down.
Their lives are already turned upside down. He's seen and/or experienced things harmful to him, and now he's acting it out on his own mother. She needs to seek help immediately.