My wife, a devoted Jehovah's Witness, gives to secular charities all the time. She undoubtedly gives money to the WTBTS as well, but not so much that I take notice. If I notice, something will change.
Is the point being made that the Watchtower doesn't exercise charity outside of its membership? That may be accurate. I am not aware of any Watchtower soup kitchens. Although I do recall them trumpeting some humanitarian efforts decades ago, I hear nothing about that sort of thing these days. The WTBTS was one of the first organisations into Haiti a year ago, but that was to look after their own. When I pointed out this little detail to my wife, she defended the Society by saying, "It's because they are family. If there was a disaster on your sister's street, wouldn't you go to her house first?" Yes, as a matter of fact, I would. But when I was sure she was ok, I'd be going to the houses of her neighbours, too. I don't think this happened with the Watchtower in Haiti. The other irony in her statement, of course, is that those who are in the Society are treated like family while those who are really family who decide to leave are not treated like family.