That's an overstatement of what he said. He had been posting about possible medical treatments [1], which is why the tweet you linked to starts with "That said" before talking about panicking and redirecting medical resources away from people who need it.
Do you know why? The drug he was posting about before that tweet, `chloroquine`, is already facing shortages around the globe for people already on it for non-COVID-19 treatments, including people suffering from Lupus [2].
He probably got attacked for promoting it in previous tweets, which is the likely context of the one you linked to, and is regardless a very valid concern for a popular figure tweeting about possible treatments. I've seen others telling people to be cautious promoting it, as we don't need people also needlessly hoarding a critical drug which is quickly becoming a frontline treatment for Coronavirus.