In almost every other manga this would be the real deal. Here, we are probably getting another date arc that will lead Mizuhara to think that maybe she could start consider thinking about the idea of maybe seeing him outside of work.
Regarding Kazuya, yeah, it's normal to be nervous when your crush that is apparently completely out of your league asks you out, but I don't need 4 pages to show that. A couple of panels are enough.