This is interesting. Try posting more tweets to articles about actors and actresses that are not in the news. That may help you to pinpoint G's methodology. It could be that G grabs the most current Tweet to display about a topic, or it could be a random selection thing. It might also be related to the fact that the performer's name is the first words in the Tweet, which could give it more weight just like an HTML title tag. Or it could be due to the strength of the theme that you are forming on the article pages.
You might be on to something Sami. You just need to figure out G's formula for selecting Tweets.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin