Those review are rating-only, meaning the customer did not leave a comment with the review. The customer simply gave you stars and that's it!
If you enable smart responses, and set the smart response template to auto-respond, you can automatically respond to positive, rating-only reviews.
It's a great way to respond to more reviews without any extra work! And since the customer didn't leave any details about their experience, it's okay to use a more generic response!