I've never heard of reviews on a hidden Airbnb, but I am responding to your post so that it's bumped, and others will see it. Hopefully, they can provide some good information.
@Kathy902@Debra300 Oh! I think I just figured it out. The guest said " I have a lot of positive reviews on Hidden by Airbnb" .
That means the guest said they had reviews on some other site, but the name of that site was blocked in the message by the Airbnb algorithms. Maybe they said "on VRBO" or "on Booking.com".