I assume it's automated. I know it's for "interesting questions." Just curious if it's a matter of views, upvotes, or something else.
I think it has something to do with the number of votes and the diversity of voters a question gets. If you get a number of upvotes in quick succession because your question is really exciting, it's likely to be tweeted. I also think a diversity of voters help the likelihood of being tweeted; 5 votes from 5 people is better than 5 votes from 2 people. You'll notice that certain types of tags which get a lot of voting, particularly single-word-requests, are particularly prone to being tweeted, rising up the hotness scale, getting a lot of upvotes from cross-site traffic, so that bizzarely it leads to one's highest voted answer, the answer most "valuable to the community", to be a maybe one or two sentence dictionary definition giving a synonym.
Our StackExchange overlords have programmed a giant AI, capable of understanding (and answering) every SE question. You may have heard of the “Watson” prototype that they resold to IBM because it was performing well below expectations.
Now, they don't allow it to actually answer questions, because that would just amount to killing their Business Model, but it analyzes questions to catch the good ones, and tweets them.
- Or maybe they do. That @Robusto guy is definitely fishy.