They likely streamed from some other Plex server in the past, and that's why they're getting the email. The email specifically states that if the server owner has a plex pass, you don't need one.
I got the email earlier today and it couldn't be clearer:
As a server owner, if you elect to upgrade to a Plex Pass, anyone with access to your server can continue streaming your server content remotely as part of your subscription benefits.
Yeah unfortunately it's no guarantee that blue states are better. Many are, but not all. Colorado, California, and New York all score a 'C', still not great but much better.