More recent numbers from this blog entry (http://blogs.kqed.org/newsfix/2013/12/06/santa-clara-county-...) have the unsheltered homeless population in Santa Clara county (where four people died) at 74% of 7631 or 5647 souls living unsheltered. Four of them dying is a mortality rate of .7 people per thousand. Not a very likely reason for dying.
It isn't that surviving cold is "easy" or "hard", it isn't that unsheltered homeless folks are "ok" or "not ok", it is that death from hypothermia is a function of both exposure and duration, which is minimized in climates such as that of the Bay Area, so that the risk of death from exposure falls below that of death by being hit by a car (http://www.nbcbayarea.com/news/local/San-Jose-Leads-Bay-Area...) for example.