Probably the rat is DF person who still feels loyality for the org. Perhaps the person is trying to get reinstated, or they just feel loyal to the org, feeling they are just not worthy, but it is still their obligation to help keep the org free from apostaes. . I have relatives, who are not even jws , who will rat on their jw family. They do it as revenge. they think jw are hypocrites anyhow, so if u do anything around them , they will report u. To me this makes more sense than an active jw reporting u or being online. That would get him in trouble too.And there are former jws who are very bitter they were df, and want to make sure all the rest of us get DF too.
Sort of like the cops having a crook that they get info from.