I work in SEO, its fun - well I like it. There are many ways to help make a site get more traffic from google and one of them is by receiving links from other sites related to your product. This is a perfect way to judge popularity in a large system but it opened a door for manipulation, this kind of industrial link spam became a problem as it started providing a poor user experience and it is a way for rubbish to rise to the top of the rankings. This is a very simplistic generalization of how it works. Anyway, what Search Engine X did was release a series of "updates" to their alogorithm that identifies these links and devalues the links so the guilty sites no longer rank. This has led to a whole buch of theories that it is now possible to "take people out" using negative SEO techniques. SEO HITMEN basically - I think this is rubbish but that is another conversation.
So here is my theory: These updates were randomized completely and caused a stir in the SEO community, basically the updates were designed for people to report spam, aggressively so now search engine X has a great base from which to judge sites and add a drop in rankings accross the board. Webmaster panic reads the forums - deletes links and submits disavow - guy on other side laughs and says - these are also spam are they not? Webmaster runs around deleting more links and telling Matthew Knife all the secret spam sites they have been using for the last ten years. When the first few updates were release there were "softenings" later on i.e. do nothing and your ranks come back - sometimes better. a clue?
This article is obviously not serious but - it does illustrate how easy it is to use unrelated incidents and paint a convincing picture when you are on the outside looking in.