When did your patient have thier x-rays? I only ask because I had a patient that had a Jones fracture (of the head of the 5th Met) and initially it was missed by the club doctor and at A&E, it wasn't getting better so he went back to A&E and they found a break.
If you are not happy with your findings always get it checked out in my opinion.
Another thing to try is that when you are doing the passive movements look at your hand positions, are you applying pressure on the sore area, if this is possible change your grip and see the outcome