1) It's a tweet (of all things)..
2) Which incites nothing, and is an expression of opinion
And the guy gets hauled off to jail for 2 months because of it? This is the kind of behavior I'd expect from China, not an ostensibly first world nation!
*edit
I meant that literally, too. My mind simply ceases processing the circumstances under which a completely harmless tweet, in a place like Great Britain, can be grounds for legal action. I thought (mistakenly) that freedom of speech was recognized a bit more with the US's allies.