What the gerrer rebbe did was that he minimized the sins of another Jew, who was going to travel anyway. Also, giving directions isn’t directly encouraging him to sin, since you could walk instead of drive.
you cant overturn halachos in gemara and shu”a of “misayaeh lidei ovrei aveirah”, helping somoene sin when it’s not a deoraysoh of lifnei iver, just because of a story from the gerrer rebbe; rather it’s the story that needs to be understood.