I read both definitions (pornography and prostitution) and there seems that there is some intersection in the definitions. A good old Venn diagram would illustrate where the definitions intersect when the person is paid for sex.
That said, this issue has been discussed before the courts and pornography is deemed to be acting since the purpose of the act is to produce pornography (art) and not simply the delivery of the sexual act.
So you can argue semantics, and based on the definitions of the words you do have an argument, but you should consider the court's opinion as these are the experts (lawyers and judges spent years arguing and weighing the facts).
That said, I'm not sure why anyone would be deemed to having voided any of their rights by participating in either porn or prostitution. Judging these people says as much about the insecurities of the ones judging than it does about the persons participating.
Unfortunately, Sherdog is full of young insecure males who feel better about themselves when they can put others down. Misogyny is rampant here as we have a huge number of incels who need to lash out at the women they desire and who think that women have to comply to their (the incels) own morality in order to be deserving of respect.