I went back and checked, that was like the 3rd time they'd been to that place? What the fuck lady... how do you know if a person is phoning it in by the 3rd time? Screw that lady.
Well that's the point, that he IS actually "phoning it in".
Heck he said so himself, the whole reason he started making art was because he wanted to draw lewd stuff, that was the source of his creativity, and now that he is with her he is doing his best to "kill" that part of him because he is afraid that she'll dump him because of it.
He is stifling the source of his creativity and that reflects on his work, and the teacher apparently can tell.
All in all this seems to be the ark where Toyoda will have to realize that Inuyama is actively trying to change for her sake, just so she won't hate him and dump him. And if the manga keeps going with the feel good happy vibes it has been going so far, then probably she'll accept him for who he is.