I'm not sure I like this line of reasoning because it implies that the ants aren't aware of us. Certainly they are in some cases. Ants are able to physically perceive us. So if aliens aren't using some means of passive remote sensing to study us then I don't see why we wouldn't also notice them (though they may have good reason to not use active means). Sure, the ants aren't aware of what why we're hanging out around them, but they are aware of us.