Not all mountain lions flee.
The following attack on on six-year-old boy (hiking with a large group of adults) occurred in the same Santa Cruz Mountains as the study above about three years ago:
http://abc7news.com/news/mountain-lion-attacks-child-on-hiking-trail-in-cupertino/298481/The study above has a flaw in thinking the mountain lions are afraid of humans at all times. The response to the piped in human voices probably startled those mountain lions in the study because they hadn't detected the presence of any humans (by sight, sounds or scents) while retuning to the kill site. Hence they were taken by surprise when they heard the human voices and instinctively fled until they could sort the situation out.
Leave No Trace