If a shadow card like this is resolved,this means only that I must place the damage on a hero?I am almost sure this is the way ,but I had seen a video where the player deals a new shadow card.

Yes, and no idea, I don't watch lotr lcg videos.

Hero Balin allows you to pay one resource to cancel a shadow and replace with another shadow card (once per attack). This is exactly the sort of shadow Balin would want to cancel, perhaps you watched a video with him as one of the heroes?

If you share us a link and timestamp in the video we may be able to provide a better answer.

... or caught a cheater!