Earlier quoted context omitted.
Static in the sense that it always executes the one function (doesn't load it from disk, its part of the executable) and so there is never any risk that some other path might get you 'out' of the docs directory and into the cgi_bin directory. So in this case static is code for 'compiled in' versus 'dynamically loaded.'
I'm more familiar with Windows, but Linux should be similar. If your application is executed often, then it's pages should be in memory already, and not necessarily need to be read from disk. In terms of execution, if it's a compiled binary, it should be fast enough, if you need more, what you want is a lightweight application server anyway.
Basically FastCGI is like having another server just for your dynamic content while the web server sits in front of it and takes care of hosting the static content and deferring to the FastCGI server when appropriate.