There's a proverb that says "You can't make a silk purse out of a sow's ear." That's because the ear of a sow (pig) is rough, hairy and generally rather coarse. ..pretty much the opposite of silk.
The idea of a pig's ear then took on the meaning af anything that wasn't particularly nice or as it should be.
Pig's eye, pig's ear or pig's ar$e were all used - especially in Australia - to mean the same thing...a mess-up.