Yes, but why tip his hand in any way? Geary gave him until noon tomoorow to answer. Why not take any advantage of that possible? Also, why risk antagonizing Geary with his answer? It just seems an unnecessary and unintelligent thing to say.
Well Geary went out of his way to insult Mike personally. He wasn't worried about antagonizing Michael. He underestimated Michael and the Corleone power. So perhaps Michael took it personally and replied with equal condescension. As Michael had likely already decided how he would handle Geary if there were any problems this could have been a source of amusement to Michael.
