When the same sample was asked the follow-up question ‘Are you religious?’, only 29% of the same people said ‘Yes’ while 65% said ‘No’, meaning over half of those whom the census would count as having a religion said they were not religious.
Less than half (48%) of those who ticked ‘Christian’ said they believed that Jesus Christ was a real person who died and came back to life and was the son of God.
Très interesting! I should have known.
If you do a "what is your religion" question, you take out the people who expressly identify as something else (in no particular order, Jews, Muslims, Ba'hais, Sikhs. etc).
You don't necessarily get all the weak/negative atheists, unless your survey is conducted in a philosophical debating society! 
(Weak/negative atheist is not a pejorative term, or at least I'm not using it that way. It means someone who lacks a belief in a deity's existence. Strong/positive atheists both lack belief in a deity and actively have a belief that there is no deity.)
For example, my mother, who has vocally said and repeatedly said before that she thinks Jesus was a historical figure and not divine , now ticks Christian, and wears a cross she bought from Primark everywhere. She now says she thinks she always was a Christian. What she means is that she likes the values of the New Testament. (To be fair, she has always appreciated them, which is why I grew up familiar with the gospels). She is also scared of sharia law, and she wants to demonstrate her rejection of Islam. So that is playing a part in it.
I, myself, many, many years ago, would have ticked Christian at one point, because back then, I would have thought cultural familiarity with Bible stories, my fear of eternal flames and damnation after death, and my feeling of discomfort at the idea of a non-Christian burial was enough.
But that really isn't the same as believing that Jesus was divine.