Question: If you choose an answer to this question at random what is the chance that you will be correct?
Answer: A premise of the show is that each question has one correct answer listed. Therefore the two 25% answers are not viable answers. With there being only two viable answers, you have a 50% chance of being correct if you guess between them.
It says you choose an answer at random, though, not choose from viable answers.
I think this is just a way for the studio execs to keep their million dollars.