You have set a minimum star rating for reviews, but older reviews below that rating still appear on your site.
Why this happens. The minimum star rating setting applies only to reviews imported after the setting is saved. Reviews that were already on your site before you changed the setting stay visible until they are manually removed.
What you can do. To clean up the existing low-rated reviews, contact support and ask them to remove the ones below your threshold. Once those are removed, new reviews that fall below your minimum are not imported.