1st - You can post almost anything you want on Twitter (with rare exceptions). Its called freedom of speech.
2nd - Not agreeing with a government, even attacking your government openly for perceived misconduct, is not a crime if you don't break a law doing so- unless you live in a fascist or otherwise totalitarian country. It's called executing your democratic rights, and responsible journalism.
3rd - Anything you say on twitter is public. Anyone who followed that person from the start does have that information already (or don't they?). In fact, anything you say or do on the internet is as public as doing in the middle of Trafalgar square.
4th - Governments do have certain rights and possibilities if they are manifested in that countries law. The question is with which intention it does make use of them- and if the populace has a chance to change those rights if there is a majority for it. It doesn't get more democratic than that.
So the problem is not the government getting information illegally. It is totally legal for the government to obtain this information.
It is also not the possibility that it may find something incriminating as that person has the right to say whatever she wants. And even to do, again as long as she doesn't break any law in the country she moves about.
The problem is a government intimidating and bullying "annoying" people by raiding their homes and confiscating their property (journalists computers seized), harassing them with prolonged and exaggerated use of administrative procedures (security consultants detained, searched and questioned at airports), and sending them 'messages' by intruding into peoples privacy just to show they can (this case).
The message between the lines is: we have the power, you have no chance against us.We know who you are, what you do and where to find you. You better be careful what you do and say, or else...
It's sad, and frankly frightening, to see just how far things have gone in the country that claims to be worlds safe guardian for freedom and democracy.