Compressed volatility and a re-energized AI trade showed strength in a month that typically exudes weakness, says Charles Schwab's Joe Mazzola, who breaks down the latest STAX report. He points to an uptick in call buying activity as a clear signal of that optimism but warns it also leads to violent pullbacks, seen in last Friday's sell-off. Joe adds that AI chips led momentum with three of the top stock buys being Nvidia (NVDA), Micron (MU), and Intel (INTC).