I see it differently.
One, I think he is ready to disclose to the therapist about the porn. And maybe more. He wants to present it to himself, as instrumental. Like I only did it for the reward that I manipulated out of them.
My concern would not be so much about the manipulation--because after all it is not true manipulating. He is up front. It is more like an exchange.
I would be more concerned about this friend. The thought crossed my mind that there might be some kind of sexual behavior with the friend. Like he is disclosing something in a roundabout and concealed way.
In any event, the therapist should be told. Your stepson is way better off having verbalized this.
By the way, I cannot understand your husband's refusal to believe his son could manipulate like this. Just mine?
I mean, your husband needs to prepare himself for what may come. Our kids are not served by our denial. Not mine. Not his.