TIOBE has always been a joke, and only even attempt to manage language chatter, not usage. It is based off job boards and internet search trends, and is highly susceptible to homonym confusion, which is especially harmul in the case of "go".
The key to Googlability for everything is to put the right context keywords. Nobody just google's "go" (or "java" for that matter). They google stuff like "go string type", "go programming", "go install", etc.
That said, the bare "go" search term gives the go website as the fourth result in Google when I try it.
I think if you could Google when Python was in it's infancy, you would get 100s results for pythons (the snakes) before you saw Python pages...
Google search algorithm is not so naive as to understand "go" as a generic token only. It can tell from context which pages are related to "go" the language and which merely use the verb "go". The reverse is how old engines used to work, Altavista and co, where you had tons of irrelevant exact matches.
2. It lets you fiddle with the 'normalized comparison' to weight the sources differently. If you play right, you can make your favorite language win!
Not sure if stackoverflow tags are a great indicator. TIOBE tries to use job listings and google trends. Searching job listings/search engines for 'go' probably wouldn't return much results (because of the ambiguous name) which is why its a lot lower than it should be.
The two are not mutually exclusive. Rather, I'd think they're directly proportional. A very straightforward and simple yet popular language should have very few questions, which doesn't seem to be the case; conversely, brainfuck is particularly cryptic and should have many questions, yet it does not.
StackOverflow is admittedly .NET heavy, but since SV is somewhat anti-Microsoft, perhaps this will balance things out.