86% of Tesla's shares are held by insiders or institutions. I don't know any retail investors that have the WSJ's ear, or think that a news article is all it takes to tank the stock.
Stock prices don't move only when a large percentage of stock is traded. When a few % are sold based on negative news, the stock price can already take significant hits.
It may not be the retail investors causing the swings but the algorithms trained to gauge sentiment from news sources and trade based on that sentiment. Wild guess.
It's this. They scrape news articles and make trading decisions based off of them. There would be a similar drop from naive systems if someone posted "Tesla Bad :(" on Bloomberg.