the answer is that the sound is better heard in the bad ear b/c the good ear hears background noise. basically, the bad ear had conduction problems b/c it was missing the middle ear/bones. the cochlea was intact. as u know, sound from outside goes through the ear canal/bones to get to the cochlea, which senses mechanical vibrations as noise. the bad ear cannot hear b/c sound from outside cannot get to the inner ear/cochlea b/c its missing the typanic membrane/middle ear bones. tuning fork to head produces vibrations through the bone that the cochlea senses in the bad ear. the bad ear can hear b/c these pressure vibrations are felt thru the bone and unlike outside noises, do not need to be transmitted through the defective auditory canal.
the good ear also senses these vibrations that go directly to the cochlea. however, the good ear also hears background noise from the surroundings (b/c its ear canal/middle ear is intact). so in short: better sound fr tuning fork in bad ear due to less background noise there.