The incidence rate probably increases with age—if they extended this study to ~26 the number would be closer to 80 or 90 percent of people sending/recieving sexts. It’s probably under 10% for the 12 year olds and over 50% for the 17 year olds—which matches the trend for the average age of losing your virginity, at around 17.

The sextortion thing is interesting but probably not a statistical outlier. But otherwise nothing here seems out of the ordinary when mapped onto general trends of sexual development.