Isn't it all subjective in the end because nobody really makes their trades with verifiable notes expressing the exact reason. So we can only guess right?
Precedent and timing. Rates-related news is always going to massively shift the market, and the market shifting right after the jobs report is a pretty clear signal.
Moreover, S&P holding course wasn't new information–there was zero evidence of anyone pre-trading a rebalancing, which means the market didn't expect S&P to materially change its rules.