The PSA score doesn't mean anything now he has been diagnosed - it is simply a marker that there might be a problem and more investigation is needed. Clearly that worked in your dad's case as he went on to be diagnosed.
I am not sure how they would know it has spread before he has his bone scan, unless it was a collapsing bone that led to the PSA test? Could they have said just that they suspect it is in his bones?
Nothing very depressing to tell you at the minute - important to get the full diagnosis details with Gleason score, staging (starts with a T number) etc but we have men who have done very well on hormones for 10 or more years so it may yet be that something else gets your dad before the cancer does.