In Us (2019), Gabe and his family are watching news which shows evil doppleganger attacking people with scissors:
Gabe: And they look like us.
Adelaide: They don't even know that yet.
Why did Adelaide think that Tethered didn’t know that they looked alike?
I believe that the "they" she refers to in that situation was the news people who were reporting on the attacks; not the tethered. She was commenting on the fact that the news was reporting these random attacks, but the news didn't mention anything about the people who were attacking looking like those who were being attacked.
