In my opinion (I kite locally) the foam has been by far the most important if not the single factor that caused their death. Other factors were very well known to the victims.
Reportedly strong currents pushed them in the foam and a wind turning suddenly created a thicker layer than was there moments before (by blowing beached foam back to the Sea).
All victims choked/drowned in the 1 meter thick foam layer. After getting in there was simply no way of getting a breath of air, just foam... Without assistance of a voluminous board or kite it must have been impossible to get their heads above foam level. The complete disorientation within the foam layer has made is very unlike to get out once in. We can only speculate how much time conscious and mobile they would have had to try to escape the foam, but it is clear it was very limited. Out of a group of 6 that went into the water only one survived. Reportedly he paddle further out to the sea instead of trying to get to shore when he found himself in the thick foam layer.

The whole community of watersport/brandingssport (shore break sports) enthusiast is devastated, as well as many others. I think very few of us would have factored this particular danger of choking/drowning in foam into their equation of risk assessment. We consequently all realize this could have happened to almost all of us (Surfer, swimmers, kitesurfers, windsurfers etc). Rest in peace. This spot will never feel the same for me.