I've been using Instapaper since pretty much the first day, and my information is not in the file. Not to say they don't have it, but, it's not in that file, FWIW.
According to one report [1], only 1 million of about 12 million stored records were released by AntiSec, so the absence of your record is not conclusive.
1: http://thenextweb.com/2012/09/04/antisec-hackers-leak-100000...