So who decides what is public interest or not?

Twitter has millions of users. We provide some private data to them. Shouldn't we know what is being discussed privately on how they will use it?

When it has to do with the government, the public has a right to expect transparency. With a private organization, its different.

Torture? Business plans? Are you seriously suggesting that people can't tell the difference?

Yes, if the documents only related to how twitter intends to treat UGC, then you would have a point.