“Hinata, are you Anbu?”
Naruto notices Hinata constantly following him. He wonders why she’s doing that. The only other instance of girls following a boy he knows about is Sasuke’s fan girls. But there’s no way Hinata is his fan girl, she’s out of his league.
He then remembers the masked Anbu agent. When he was much younger they were far more overt. Their presence became subtler as he got older but he always knew they were present in some capacity watching him.
He concludes that Hinata must be a new Anbu agent assigned to monitor him at all times since she wouldn’t arouse suspicion as a kid his age.
He confronts Hinata over this. She embarrassingly goes along with the lie viewing as a way of saving face.
Naruto is ecstatic to have his own Anbu agent following him. He believes he’s closer in his goal of becoming Hokage since only important people have Anbu agents following him.
He also believes Hinata must be a super strong ninja and her underperformance in class was simply an act to feign weakness. She also acts gloomy and insecure to divert eyes from her so she can remain discreet.
Hinata (barely holding back tears) confirm this. Naruto doesn’t notice the look on her face congratulating himself on being smart enough to figure it out.
Hinata now has to fake being an Anbu agent.
Bonus: Naruto’s actual Anbu patrol sees this and adopts Hinata as a little sister to help her out finding this funny and long shipping her with Naruto from seeing her follow him everywhere.