No one ever said he did. That would be blasphemy. Reformed Christians believe Jesus Christ.
But ye believe not, because ye are not of my sheep, as I said unto you. My sheep hear my voice, and I know them, and they follow me: And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand." -- John 10:14;26-29"I am the good shepherd, and know my sheep, and am known of mine.
Note the sheep follow Christ not because they know Him, but because He knows them.
So how do you know you are a "sheep", then? Your passage speaks about God's point of view, not ours.
Regards