If advertisers discovered that there are more bots on Twitter than they were told (and consequently that the audience of real humans is smaller than they were told) future revenue would probably decrease.
Sorry for not being clearer. I wasn't suggesting that the stock price dropping was an MAE. I was suggesting that the thing that caused the stock price to drop could arguably be an MAE. That's the whole point of my comment — there would be an argument about causation between the revelation/accusation, the stock price, and anticipated impact on revenue (as a sibling commenter pointed out).