Rise: Collaborating with an Outside Vendor

We're having an outside vendor work on a batch of Rise courses for us, and the files are ready to transfer back to us. However, I'm seeing something that I didn't think was possible in Rise: Collaborating on a file with someone outside your team/company.
Rather than the files coming back via the Send a copy route, it looks like they're inviting me as a collaborator and then transferring ownership to me. They're still listed as a collaborator on the files.

Is what I'm seeing correct and by design? Are we able to collaborate on files with users outside our team/company?
I vaguely remember seeing another forum thread stating that this isn't possible, but I can't seem to find it anymore.