I have been wondering if the Rakuten Cafe background was edited later, and I am almost sure now that it was edited in. There is no way that no one looks at her, and singing quietly is hard.
No. Her right hand is behind the chair back (watch closely), and several people look at her starting at 37:00.
Besides, remember that this is Japan: it's part of their cultural conditioning not to make spectacles of themselves or to interfere in other people's business. When they see a camera crew, they either try to look busy or simply get out of the way.
Oh forgot to mention it too, it was really great never see something awesome in H!P before. Hmm i'm confused are those in black Coats °C-ute or the KKS. Because you don't see anything besides those Screens with their Close-Up's. Nonetheless it was just great! Mizukis Performance was sweet. She's not my fav. but she's a good Singer.