Hogwash. Pretty much every company on the S&P 500 dropped 30% around March. Did their perceived long-term value change 30%? I doubt it. I think most people were fully aware that most companies in the S&P's 10 year value wasn't going to change much; certainly not 30%. Yet, it dropped 30%. And then the next month it has risen back up to about 10% of its all-time high. I don't think people seriously thought that Apple, Coca-Cola, Pepsi, etc. suddenly dropped in value 30% and then suddenly rose 20% (yes, I know, technically it was more). If you can have swings of +/- 30% over a period of two months, I don't think the value is reflecting the long-term prospects.
There is both short-term AND long-term pricing in stocks. "In the short-run, the market is a voting machine. In the long-run, the market is a weighing machine." Ben Graham