It's just black and white, there's no AA on the textures. The eye can just be tricked by how dense the textures are. Unless I don't understand something about how unity renders textures which is possible. But none of the textures themselves (besides a single one that was given to me really compressed) have any grey on them or AA to fuzz them up. If you blow the textures up in size they're very clearly 2 colors. But just to clear up confusion I'll blow them up a bit because it's possible some monitors may blur them together.
I should have said, I didn’t just eyeball it, I copied a screenshot into an image editor to check. (I used that same technique for my game to find places where I accidentally used more colors.) One example is the gun in the lower right has shades of gray. I can post a screenshot later.
Edit: https://imgur.com/a/nRyfdDu It's even in the dithered part. I used the Win+Shift+S tool that's built in to Windows to screenshot the game, which I don't believe adds any extra AA to the image but I could be wrong. Does the game have a built in screenshotting feature?