I was a JW long enough to know that you don’t get to sin in one congregation, hold onto the info just long enough to transfer to a new congregation, and then confess. Shady action like that is enough for them to conclude you aren’t really repentant and are looking to escape punishment. Chances are they make you go back to the nearby congregation you just fled to face a JC.
Chances are he might have even avoided a JC for something as simple as sexting especially when and "if" no one else in the congregation was involved. As you said, this looks unrelated to the online porn chatting and something else. Something that "Tom" in Croatia was worried about months or years after. If porneia was involved then any JC would have deliberated after Dijana's decision. If Dijana would have not forgiven him chances were that he could face disfellowshipping. What could a young and unexperienced Dijana do alone in a foreign country? Again as you said there are crucial missing points here and the ones offered in his memoir are contradictory and inconsistent with WT policies.