Only if his argument is compelling to people with enough money to drive the price. The average investor doesn't even know how to short stocks.
1. Media person shorts stock
2. Media person tells viewers stock is worthless
3. Viewers holding stock get nervous, sell shares
4. Stock price goes down, media person cashes in.
I do think it is a bit unfair to say they need to hold their investments in a blind trust, but definitely agree that disclosures about their positions should clear and abundant.