no, it's not. It's the dumbed down "truth" so that you can explain to
random people what the hell Unix is, or rather to make them have a
dumb look on their face and nod.
A process is not a file, a memory region is not a file, the sysctl tree
is not a file, there's plenty of stuff that is as far from files as
you can get. Many directory operations are explicitly not done on file
descriptors because it would be too complicated.
//art