Of course you are right, Scot, that there must be publication to someone other than OrganicCloud. But whether there has been is less than 100% clear. So, for example, defamatory remarks included in a letter sent to the person defamed were held to be published to the addressee's secretary who always opened his post. Here the defamatory remark was put into a message sent to this site. Can anyone other than OrganicCloud (like the secretary in the letter case) see the message? I don't know. Pehaps they can. The site wants people to follow its rules so perhaps messages are monitored. I don't know and neither, I think, does Shenanigns.
The mere potential for someone else to see the message would not be enough. You would have to find someone who actually had seen it. Difficult evidence to find I imagine.

It's not a moot point. It can't be defamation if he only communicated it to the person the accusation was aimed at. End of story.
Read even basic information on it. You're wrong.