Most day traders close all their positions at the end of each trading day, so as not to be exposed to overnight gap risk. (A "gap" is when the opening price in the morning is not equal to the previous day's closing price. These occur when relevant news arrives after the 4pm ET close.) So if he was really a day trader, he would have been in cash.

It's possible he had been spoiled by the big bull market and didn't know how to trade successfully in a bear market. Different tactics are required.