what has winston discovered when he says the proles are the human beings. we are not human
I was unable to find a quotation in Chapter 7 of George Orwell's 1984 stating that only the proles are "human." Perhaps you are referring to this quotation:
’Proles and animals are free.’
The "proles" are the simple laborers in Orwell's dystopian world. They constitute 80% of the population; the other 20% are members of the ruling "Party."
Although the proles must work hard to earn their meager salaries, Orwell's hero, Winston Smith, feels that, in a certain sense, only the proles are free.
Party members live drab lives in which every action is dictated and monitored by the Party. They are even discouraged from finding pleasure in their sex lives. As Winston says:
The ideal set up by the Partywas something huge, terrible, and glittering — a world of steel and concrete, ofmonstrous machines and terrifying weapons — a nation of warriors and fanatics,marching forward in perfect unity, all thinking the same thoughts and shoutingthe same slogans, perpetually working, ﬁghting, triumphing, persecuting —three hundred million people all with the same face.
By contrast, the proles are permitted to live a more natural and normal life:
They were born, they grew up in the gutters, they went to work at twelve, they passed through a brief blossoming-period of beauty and sexual desire, they married at twenty, they were middle-aged at thirty, they died, for the most part, at sixty. Heavy physical work, the care of home and children, petty quarrels with neighbours, ﬁlms, football, beer, and above all, gambling, ﬁlled up the horizon of their minds.
Such a life does not sound very exciting or intellectually stimulating, but it does allow people to satisfy their most primal desires without being dictated to or observed by the Party.
This is what Winston Smith means when he says that only the proles are free; if being human means to be free, then only proles are human.