They knew the individual. They certainly did not "know" him as the "Son of God" (utter blasphemy) but as a one of many messianic claimants.
When Jesus came into the coasts of Caesarea Philippi, he asked his diciples, saying, 'Whom do men say that I the Son of man am'?
And they said, Some say that thou art John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.
He said unto them, But whom say ye that I am?
And Simon Peter answered and said, 'Thou art the Christ, the Son of the living God,
And Jesus answered and said unto him, Blessed art thou, Simon Barjona; for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.
The Gospel of Matthew Ch. 16 v. 13-17
Peter knew who Jesus was for as it is written in the Holy Scriptures, so shall it be.