You are correct; the Church does require that weddings take place in a church. Only by dispensation may they take place elsewhere. Any priest (including a bishop) who wants to officiate at a wedding within a particular parish must obtain faculties (permission) from the pastor of that parish for the marriage to be valid. Should he want to officiate at a wedding outside of a church, he must obtain permission from the ordinary (bishop) of the diocese in which the wedding is to take place.
Anyone who expects to get married in the Catholic Church is required to join a marriage preparation program in a Catholic parish. This whole thing sounds very fishy.
Get the name of the bishop. You can check with your local diocese as to whether he is real or not. Also, if the couple is not being prepared in a local parish, you know that the bishop is a phony. If you need more help, let us know.
Fr. Vincent Serpa, O.P.