Berkshire's performance has been pretty much identical to the average S&P 500 stock in the last 7, 8, 9 months.

We are talking about the last month/4 weeks. During that time there was nothing identical at all. Instead a sharply(!) rising Berkshire, in sharp contrast to the months before --- and the "coincidence" that this rally started exactly(!) when the Nasdaq started to fall.

To explain that away by "pretty much identical to the average S&P 500 stock in the last 7, 8, 9 months" you have not only to believe that Berkshire during that 1 month interval just caught up with the total rise of the market during the months 7, 8, 9 months before.

You additionally(!) have to believe that said perfectly identically timed negative correlation to the Nasdaq is pure coincidence. This is the opposite of "One simple explanation is that there is no explanation needed": It´s an explanation, and one which requires too many assumptions for my taste. Anyway. You have your opinion, I have mine, and apparently we won´t agree :)