When you click on someone's profile, up at the upper right it shows how many people they follow, and how many follow them. Then if you click on a post, over on the right hand side it shows a few replies, and at the bottom how many people retweeted it. For that post, Twitter said it had been retweeted 100+ times...I think that's as high as they go.
So I think it was an example of the spread of the Internet. A few people saw it, retweeted it, and then more people saw it, retweeted....before you know it, a whole passel of people are talking about it.