Can you quote a paragraph you didn't like? Is your main issue that the data descriptor is defined elsewhere (as opposed to a date range)? I don't think the descriptor itself is emotional at all.
By the way, I thought based on the abstract that the effect would be rather large. For anyone who downloads the PDF, go to the graphs - the effect is actually a very small difference even on search terms rated to get people in trouble with their governmetn, as well as on personal-privacy related search terms.
The effect is clearly there but rather small compared to what I was expecting.
Granted I only spent a few minutes with the PDF and could be misinterpreting.
"After PRISM Revelations" simply means "After PRISM was revealed", since it was hidden from the public before. So, Snowden revealed the existence and scope of PRISM to the group of people whose search behavior this study is analyzing (the general public).
Not an emotional word and, overall, not bad writing in the study.