Oushi appears to be talking about "Sealing the view with the object of emptiness". This means that once a person has realized the truth of emptiness, rather than abiding within that emptiness without any conceptualization about it, they start labeling everything as "empty". This is empty, that is empty, I am empty, look at all the empty things!
Everything is empty, according to Buddhism. How could one thing be empty but not something else?
Sealing the view with the object of emptiness involves a conceptualization of emptiness rather than a direct realization of it. For example, someone sees an object and thinks "This object is empty" but that is *not* the experience of emptiness, nor its realization, just an intellectual understanding. Abiding in emptiness, there is no concept of it, nor are there any objects to label as being "empty" anymore because one is no longer engaging in mental projection, as the mind has withdrawn into its own true nature and mental projection and fixation has stopped.
According to Buddhism everything is empty, so if what you're saying is true then all Buddhist who haven't realized and 'abide' in emptiness are nihilists.That isn't right, right?
Not exactly. The difference is in whether or not the individual is aware that they only have an intellectual understanding. Its one thing to contemplate objects of the mind, which have been reified as real, and think "This object is empty" and in that way examine how and why its empty. Thats an intellectual process, and an important one. It can lead to realization of emptiness itself once conceptual elaborations are dropped, but the realization itself will be non-conceptual. This is in line with Buddhism and it is taught as a strictly intellectual exercise.
When someone only has an intellectual understanding of emptiness but thinks they have realized emptiness itself, then they become Nihilists because they have reified emptiness as being an object of the mind, which it is not. Therefore they "see" an object, which has been non-existent from the very beginning, and they "label" it as being "empty". This is a mistake.