Hedge fund manager Stanley Druckenmiller said Friday he agrees with fellow billionaire investor David Tepper's optimism on the market and said he, too, is still "riding the horse." "I revealed a very bullish posture intermediate term since October when [Fed Chairman Jerome] Powell guaranteed he would not rescind the insurance cuts," Druckenmiller said in an email to CNBC's Joe Kernen. "Since then, both have worked out and the Fed is still whining about inflation being below target."