Clark is making it easy for Luthor to find the truth (that the Italy story is bogus) and give it to Lois on a silver plate, making Luthor look like the truthful and trusty friend that is saving her from a lying and crooked partner.
In Clark's defense, he never told her the Italy story. He also does not know she overheard it.
Still, I have to agree his plan is flawed. I think he should have already told her.
