Actually if you look at the stocks where he posts, they are just as liable to go up as down but people have a confirmation bias when it comes to him and only remember when the stock goes down and do not pay any attention to his videos when stocks go up.
I have seem him post on stocks that have gone on mega runs. Look at his postings, he posts on tons of stocks you will find that he has no impact one way or another, all he does is post on the 10 ten forums