[Mailman-Developers] Confusing definition of "subscribers"

In /lists/, it prompts that "Only lists that you are owner,moderator or subscriber for are shown here", but I see a list which I was only sent a email to or has not request a subscription.

Also in /accounts/subscriptions/, that list appears as "nonmember", but not in the "list-based preferences".

So what's the definition of subscribers? Is it defined as who has interaction with the list?