Does the WTS still expect members to turn others in when they learn of something like this? It's a thorny issue, and I think it is usually left to an individual's conscience. But they may feel as if someone who does not report another JW is allowing 'spiritual corruption' into the congregation.
I do think that most JWs don't take an absolutist approach to this stuff, but the most devout ones would not hesitate to put the organization before family/friends. That is what a 'good Christian' would do, after all...