Well, he was wrong.

Here are some thoughts from Goldman's strat team on levels and size of flow from the Passive community which gives an idea as to what drove the accelerating market crash into today's close.

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SYSTEMATIC FLOW UPDATE…

*our (GS systematic strategist) work suggest that the 2,735 level in the S&P is where trends could start to change, driving more aggressive selling from the CTA community. We estimate this community to be long approximately $70bn of US equities and $190bn globally coming into today. If negative price action continued or worsened, we think getting flat (i.e. $190bn of global sales) in a month is reasonable
 
The difference between Risk Parity and CTAs:

Risk parity and CTAs (managed futures funds) are not synonymous: Risk parity is a long-only strategy with negatively correlated assets that is sensitive to volatility spikes in the market and positive bond/equity correlation; managed futures funds (CTAs) are long/short strategy funds aimed at capturing trends in the market (in either direction)

The conditions that could lead to forced-model selling impact CTA behavior only such that wide spread selling will generate a downward trend  

Since CTAs look to capture trends in the market, they are likely to apply additional downward pressure on markets if forced-model selling occurs

Additional pressure from CTAs may further exacerbate the sell-off from risk parity funds