He says that the market actions during the GFC when the USD rallied appreciably show that the greenback is still the place to go in times of trouble.
Another way of seeing it is that the market was over-leveraged and overly short USD when the GFC broke and as liquidity dried up, this led to massive illogical moves. The market wasn’t buying USD as a safe-haven, it was buying because it was short and was forced to cover.
That’s all water under the bridge now. An increasing number of people when faced with the choice of holding USD, EUR or even Gold are avoiding the dollar like the plague.