To the average person it means: No matter what task you apply the tool to, that you will be right 85% of the time, and 85% is a solid B, a passing grade, so let's use it.

So in other words, if you show it 100 random people and ask who did it, it will tell you to arrest 15 people, with a 15% chance not a single one of them is guilty?

(assuming it will operate independently for every individual you show it)

That's great.

Of course, putting such a system on public cameras, scanning large amounts of people, is about as stupid as some of the biggest disasters in medicine (using a 98% effective drug on random people, regardless of whether it would help them or not. You REALLY want to check what happens if you're wrong before applying it to a large number of people)