"From where he was standing, Asuna could not clearly see the details of his action due to system distance effect, so that when he does press a button, she will not know which.
Oberon used NERvGear to connect to the virtual world, but his time in the virtual world is limited. Therefore, there are a lot of things that he does not understand. For example, in the virtual world, mirrors do not comply with optics.
There, clearly reflected, is Oberon, an image with a clarity far too high. In the real world, no matter how close your eyes are to the mirror you can't see far away objects. Here the mirror is just a ultra-high resolution screen and the distance effect doesn't apply. Thus, even the activities of Oberon's fingers are clearly visible."