I always thought they were people that publicly said they were no longer jws and were actively working against the WTS by sending letters contradicting WTS doctrine to jws, talking to them about the same.
I actually watched John Ankerberg's show when a group of ex-jws were on. One said that all the copies of The Way To Paradise (VanAmburgh, 1925) had been ordered burned. Our local congregation had a copy, as did 2 jws in their personal libraries. On a visit to Bethel, I checked their library and found several copies (at the time the library was open to visitors). So that made me wonder if their other statements were true. It is important when talking to jws that you have a good foundation under what you say. That is why I say hang them with their own words.