This is Cyril of Jerusalem, and he's writing about their liturgical service for communion that they would have had every Sunday.
And he says this: "Next the deacon cries, 'Welcome one another, and let us kiss one another.'" And then Cyril continues, he describes what the deacon says in the service, and he says this—this is Cyril saying this as an explanation—"You must not suppose that this kiss is the kiss customarily exchanged in the streets by ordinary friends." So it was normal for people in the streets, non-Christians apparently, as well as Christians, when they saw a friend in the street, they would greet them with a kiss.
He says this kiss is different, affecting as it does a co-mingling of souls and mutually pledging unreserved forgiveness. Join us in earnestly contending for the faith that was once for all delivered to the saints.