It may be rare, but it certainly does occur.

Slow, gentle movements in QS generally are the best way of escaping. When you thrash around, you'll be pulled down by the vortices that you create, and once pulled down, it is difficult to surface. Best solution is to divest yourself of heavy clothing and packs, as most people naturally float when not encumbered.

that quicksand tends to form in flash flooding situations, where water does not have the opportunity to drain naturally. This adds slow moving currents to the mix. More than likely, what did the guy in was getting caught up in the flash flood then inhaling the silt laden muddy water. Parts of Colorado, where I have friends, are very similarly - very dry most of the time, but flash floods can turn deadly there quickly.

He “died” in the quicksand , but it wasn’t the cause of death.

This is more a case of shitty reporting