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.
You must understand that there are different levels of inside information, inside information is not illegal in itself, so there is nothing wrong with what he or anyone is doing, in fact if you are a fundamental investor you want to have as much information as you can before making any kind of investment in a company, and with his reputation it is obvious to me that even if he forgot everything about how to invest he will still very successful since he will have trusted people to him giving him hot tips about which company to select to invest.
Inside information actually is illegal. Information is either public or it is not. If it is not public, it is inside information, and inside information is illegal to use for trading purposes. Just because a particular person doesn't know something doesn't mean it's not public though. If the information is obtainable and someone doesn't know how to find it or doesn't, that doesn't mean it's inside information. But information that IS insider information is without question illegal to trade on.