Can anyone explain to me where the vaccuum in the engine block comes from?
There is no vaccuum in there! Unless air is magically expelled through the breather via a one-way valve that only allows air to escape, it's not a compressor.
Plus, the sock only went into the head where it could have gotten ground up by the cams, but I doubt that the fibers will kill the engine, since an engine can take off a finger and keep running without a hiccup.