Hot Trends and "QDF"

A New York Times article (Google Keeps Tweaking Its Search Engine) includes a discussion of Google's "QDF" -- "query deserves freshness" -- initiative:

"The QDF solution revolves around determining whether a topic is 'hot.' If news sites or blog posts are actively writing about a topic, the model figures that it is one for which users are more likely to want current information. The model also examines Google’s own stream of billions of search queries, which [Google engineer Amit] Singhal believes is an even better monitor of global enthusiasm about a particular subject."

Was Hot Trends a spin-off from the QDF initiative? Was it a tool that Google's engineers developed for their internal work, and now have released to the public?

Google Blogoscoped, which alerted me to this article in the first place, notes the similarity to Hot Trends. But I see more than similarity -- I suspect causation.