It was interesting reading your link to the WT apologist site. It seems their main point was to try to deflect from the fact that the WT voluntarily became associated with the UN. They are right that association with the UN did not make them an NGO. And there are many NGOs not associated with the UN. But that is hardly the point.
They also spend a lot of time determining the exact procedure involved when the WT became associated with the UN. I don't think any of that matters. The issue is that, for whatever reasons, the WT voluntarily chose to be associated with the organization they say is the wild beast of Revalation. An organization that they believe is controlled by Satan. They have spent many years claiming that the harlot, "false" religion, will be destroyed by the UN, and that part of what makes them so evil is that they are riding the wild beast.
In my opinion, voluntary association with the UN in any way and for any reason is a huge hypocricsy for the WT. They know this too, which is why they immediately withdrew as soon as they were found out.
I also felt that their excuse was pretty weak. As if the UN had the only good library in New York, and they were simply unable to get the necessary information to continue publishing their literature without it.