It is difficult to know quite what this means without seeing the actual survey questions, which may not have been formulated very clearly. The BBC's own evaluation of the situation could be clearer as well:
Many scholars agree that Jesus was a real man, who lived in Galilee more than 2,000 years ago, although many details surrounding his life are still debated.I know of no specialists (i.e., people with academic training who publish in peer-review venues) who think that Jesus did not actually exist. But, yes, there is a great deal of debate on what and how much we can know about him from our very limited sources. Some relevant posts are collected here.
And perhaps it's just me, but this article made me think of this Onion classic: Historians Admit To Inventing Ancient Greeks.
