Currently the only positive test for prostate cancer is by biopsying the prostate. And there are other causes for PSA increase besides PC. And you can have PC without high levels of PSA.
The bone density test uses a dual energy x-ray. It does not measure metastasized cancer. I really don't know, but it might also show areas that are suspect.
http://www.medicinenet.com/bone_density_scan/page2.htm
The absolute amount of bone as measured by bone mineral density (BMD) testing generally correlates with bone strength and its ability to bear weight. The BMD is measured with a dual energy x-ray absorptiometry test (referred to as a DEXA scan). By measuring BMD, it is possible to predict fracture risk in the same manner that measuring blood pressure can help predict the risk of stroke .It is important to remember that BMD cannot predict the certainty of developing a fracture. It can only predict risk. It is also important to note that a bone density scan, or test, should not be confused with a bone scan, which is a nuclear medicine test in which a radioactive tracer is injected that is used to detect tumors, cancer , fractures, and infections in the bone. The bone scan is completely different type of test.
http://www.webmd.com/a-to-z-guides/bone-scan And while it can detect cancer it can not tell the type (as far as I know).
Possibly you confused two different conditions that he want to treat you far. I would go back and true and get some more clarification.
And when you talk to him ask for specific answer and write them down. Ask for the exact name of the test. And ask for for the results indicated. And get a copy of the test. And also get a copy of your PSA test for the last few years.
You have the right to a copy all of these and in fact your whole file.
If he can't make it clear then see a urologist about the PC.