The concern would be that the hot spots could be prostate cancer metastases, usually referred to informally as "mets". These would be prostate cancer metastasized to bone, btw, not bone cancer, if that is the case.
From the information you provided, it's probably hard for anyone on this board to say exactly what the situation is, but from what you wrote it sounds likely that he has systemic disease. Hopefully he's in the care of good medical oncologist, preferably one who specializes in prostate cancer. Others here on this board can give you some names if you're interested.
IF he has systemic disease, he needs systemic treatment. The goal switches from curing the cancer to stalling it, through the use of hormone therapy (androgen deprivation, or ADT) and maybe chemo at some point. Just because he has some hot spots - even if they are from prostate cancer - doesn't mean it will progress rapidly.
There are men here and elsewhere who do very well with ADT, and go on to live happy, productive lives for many years. ADT usually causes mets to shrink or disappear from scans, and it relieves pain. Androgen deprivation deprives the cancer of the testosterone it needs, and that knocks the cancer on its can for a while--sometimes for decades. There's no guarantee, of course - some men stop responding to ADT sooner than others - but there's no reason to panic that you are about to lose your friend anytime soon.
There are others here who know a lot more about treatment of advanced disease, so I'll shut up now and let them correct any inaccuracies in my statements and tell you a lot more. I wanted to jump in here and tell you that things aren't as dreary as they may seem on the surface.
Best wishes to you and your friend.
Dx Feb 2006, PSA 9 @age 43
RRP Apr 2006 - Gleason 3+4, T2c, NX MX, pos margins
PSA 5/06 <0.1, 8/06 0.2, 12/06 0.6, 1/07 0.7.
Salvage radiation (IMRT) total dose 70.2 Gy, Jan-Mar 2007@ age 44
PSA 6/07 0.1, 9/07 and thereafter <0.1