What's the difference between Collectives and Circles?

Is there a resource to understand the different usage cases for Collectives and Circles?

Circles allows your users to create their own groups of users/colleagues/friends. Those groups of users (or ‘circles’) can then be used by any other app for sharing purpose (files, social feed, status update, messaging, …).

Collectives is a Nextcloud App for activist and community projects to organize together. Come and gather in collectives to build shared knowledge.

So collectives is a way to share knowledge (a bit like a wiki), circles is way to let users group people into “groups” (not to be confused with the nextcloud groups, that’s why it’s called a circle).

Circles are “groups” which can be defined and controlled by the users. So you can create a public circle called Sailing Club and invite people to join.

Now any other app supporting circles can have it’s data shared with the Sailing Club circle as opposed to the individual users or requiring the admin to create a group.

Collectives is collective documentation. Think of it as collaborative notes, which are built on top of circles (instead of users). This way your Sailing Club documentation will stick around even if the users leave. It is a Nextcloud equivalent of a wiki.

So am I correct in understanding that you can add people from the sailing club who are not users of the Nextcloud? Or do I need to make each of my sailing club members have a user account on Nextcloud?