How do we know that the return type was what it is?

models.go

func GetEventByID(id int64) (*Event, error) {
	query := `SELECT * FROM events WHERE id = ?`
	row := db.DB.QueryRow(query, id)

	var event Event
	err := row.Scan(&event.ID, &event.Name, &event.Description, &event.Location, &event.DateTime, &event.UserID)
	if err != nil {
		return nil, err
	}
	return &event, nil
}