A lot of Wall Street trading is automated and responds to keywords.

That tweet got a lot of coverage in the mainstream media, together with a discussion of why American insulin costs eight times what it costs in Europe and Japan and calls for regulation.

A trading bot seeing "Eli Lilly" and "regulation" in the same sentence will sell stock, because regulation means lower income streams.

And long-term, the bot might not be wrong, because insulin prices are now being discussed.