I thought 'everything is a file' mostly referred to the fact that you can read/write to every file descriptor, no matter if the file descriptor points to a sock

I thought 'everything is a file' mostly referred to the fact that you can read/write to every file descriptor, no matter if the file descriptor points to a socket, a pipe, etc., or an actual file. Before that, you had completely different syscalls depending on the device you were using.