You know, the entire "she doesn't recognize him while looking at him point blanc" could somewhat easily be explained by her having poor eyesight and not wearing glasses/contacts while at home. So of course she didn't think this hot confident teacher is actually her dumb classmate.
But this explanation opens up a whole new bag of worms that needs to be explained... Like, how do you study if you can't see shit?! Huh. Okay.
How about making Tsukiyama's disguise a little bit more elaborate. Or the girl actually has prosopagnosia. For some who never heard of it, it's a condition when you're unable to distinct human faces from one another / fail to recognize them. Doesn't need to be a severe case, just her struggling to tell people apart from each other, as for the voice, he could have tried to change that to sound more mature. Boom. Problem solved. Conflict established. Guess it's way too complex for a regular manga, much easier to portray her as an idiot.
Or we're reading way too deep into it- she knows it's him, she just gaslights herself into thinking it's someone else. Yup