The proles maintained a humanity much like our very own. However, it was a humanity that experienced emotion without thinking too deeply. The proles were allow to act much differently than Party members and kept more of the rituals that we keep today (sex was for pleasure and in relationship, not like within the Party as a duty to the Party).
The Party was ever watched and guarded. The proles were more able to roam the streets. But, all the same, the proles were controlled. This seems a little ironic to me to even call them human. They were manipulated in their thought and allowed to commit greater moral sin than Party members, so it would seem they were more free. But they weren't. They were removed from thinking about the Party and were well unaware of what it was doing. I'm not sure if that really can be called human. One of the great advantages I find in this life is the ability to think and analyze this world around me. That was taken from them. I think Winston says this quote to make us think about what it does indeed mean to be human.
What Winston means by this is the the Proles had not been subjected to the changes that the Party forced on its members. He means that the Proles get to keep having feelings and relationships in a way that he is not allowed to.
Winston really wants to have human relationships and feelings. The Proles get to do this but he does not. They get to fight over the pots and pans. They get to have families and care for them. They get left alone to have private lives. People like Winston do not and, he thinks, they are less than human because of it.