Buffet is a very clever and prominent person but it seems me tha the often has some inside information before making investing decisions but anyway I respect him very much. It seems me that he describes 2 stages of market. The first in is an oversold stage where you need to buy to reap some later and the second one is an overbought stage which is usually named as ephoria where you need to sell all your assets before a crash or a deep correction phase.