They don't mention traffic volumes at all. I would assume they're getting more traffic from Google than from Twitter. More importantly, this is from a blog for ubervu, which is a product that tracks the social web...has it occurred to them that perhaps the demographic that uses Twitter would be more amenable to their message than the broad demographic Google services?
It is a case study. It doesn't mean it's the same for every website out there. That's in the article. Of course the website is more appealing for Twitter users. It says that in the article as well.
To answer your question. uberVU gets more traffic from Google than from Twitter.
