No, Kacy, I don't think they adjust the scores based on the scores of those who are taking it, I think it's set. Your score probably fluctated because you answered some questions differently.
Did they say anything about the validity of this test during the show? I know that when I saw the American version, it said it was developed by a professional psychologist, and was standardized on a general population sample so that the average was 100.
I can vouch for the reliablity of these tests, at least. I have taken two American versions of these "Test the Nation" tests, and have scored 120 each time. The Canadian version gave me 119. My SAT scores (when convereted to IQ) would give me an IQ of 120. Pretty consistent.
There's also the British version:
http://www.bbc.co.uk/testthenation/iq/
I took it, and if I remember correctly I got 109. I know that the difference in language/culture accounted for at least a couple of missed questions.