You can't just use search engine queries as a proxy for popularity, especially on something like a website. Is it possible that Twitter serves a more technically savvy portion of users that knows how to use the address bar in their browsers? Or that people are more interested in researching about Facebook than Twitter even if they use both?
Even if you're right on all of those things, the difference in the numbers is staggering, and what you're talking about can't really account for that big of a difference.
Also, Twitter is disproportionately popular among mobile users, many of whom don't even access it via a webbrowser. I'm not sure it's exactly the same as tech-savviness, either; I'll see if I can look it up, but I remember reading that Twitter is particularly popular among non-traditional internet users, especially African-Americans, who have a mobile device but rarely use a laptop or desktop computer. Facebook, by contrast, is mainly a website.
