I think this is for the new plan, which doesn’t differentiate users by public or private anymore. For the new pricing, there’s only a limit for personal users (defined as "users who sign into a Glide app using a consumer email domain, such as Gmail, or an education email domain, such as .edu. Editors in your team are also included.)
This was a temporary solution from Glide to handle inaccurate overage limits. You see 50 now because the migration work is completed. I think this should have been communicated better through the usage/pricing page.
I’m not sure on this one, I think it should just limit users from signing in, and as long as your row quota is under the limit, you should be able to add more.