It could be innocence and most likely is but there is more to the story with the porn addiction.

The porn addiction ( if that is possible at that age without him being a victim of sexual abuse) so young has me wondering if something was happening to him inappropriately around that age. I think your instincts are right.

I think since it is still bothering him, perhaps there is more bothering him that he doesn't realize, that maybe he should see a therapist about this.

I grew up with a few friends of the same age who were being sexually abused when I knew them but didn't know it until many decades later when they told me. I do remember their almost obsession with sex and how it works. ( like elementary school age.) They had forgotten or suppressed the memories of abuse for many years. I think they were acting out what was happening to them with other kids probably trying to figure it all out. Sex was normal to them at that age. But it WASN'T normal, something was happening to them at that young age.

It could be nothing, but since it is still bothering him (which is a clue it could be something more), a T could help him either way.