Besides Nodoka saying this, there have also been Narrator convincing Akira at the start that Nobody is real. But we also have a Narrator saying to Akira to remember everybody is real and that their story continues even when he isn't there in a Sara / Sana event. (Don't remember which)
So, we can't really take the game / Narrator's words as truth as they all seem to want to use Akira for their own ends. As for Nodoka, at that moment, she said those stuffs to get a rise out of Akira. I think Nodoka was checking if Akira was the same as her Mother. The voices inside your head fits both Akira and her mom.
well there is one important thing tho.
the novel nodoka wrote about sensei and other girls end up with sensei
waking up in a
room with clocks.
she knows everything about sensei in a mind reading level.
so we can assume she was talking about sensei not her mother.
Even the white "hope" and "angel" figures looks like doctor and nurses.
sensei's twisted mind see hospital workers as evil creatures that trying to control his mind but in reality they are just doctors trying to cure him.
well game is already drops tons of hint that nothing is real. giant walls? aliens? talking plants? come on this is either a simulation created by some sick god.
Or what a schizophrenic patient sees.
it is actually funny.. imagine a crazy naked person that thinks janitors are loli girls and trying to have sex with them, so they keep him in a room xd