[MM3-users] Odd hold message

I received a very simple post today that was held with the following reason:

The message is being held because:

Message contains administrivia

At your convenience, visit your dashboard to approve or deny the request.

What is this all about? What does Mailman consider to be administrivia, of all things, and why is this a reason to hold a message?

The only thing in the message I can see is that it mentioned '100 members'. Is Mailman becoming sentient and developing an attitude? Seriously, I'd like to know more about this.

Andrew