Maride, I just asked my DH about it and he said it could just be they didn't swab the faucet with alcohol when they took the sample!
He also said that it was not true that bleaching would just cover up the problem, rather than solving it!
I agree with the others, sounds like he's looking for an out. And since he's tied up so much time, possible loss of other offers, I truly hope you get to keep the earnest money, and recover the cost of all these tests!
Good luck!!!