(Intentionally crafted) large metadata in a video file (which can be very large anyway, so 2GB extra doesn't stand out). A string field in a (machine-generated) JSON/XML dataset. And like tomohawk says, lack of a mechanism that prevents accruing large blobs (for example not limiting the size of an incoming HTTP header in a web server).
Binary file contents are often strings, right? If you're using snprintf() to copy strings, as the thread was suggesting, there are valid reasons to try to copy such strings (though they would be few and far between).