If I have a question [???] and the answer is "true" or "false". The probability of it being "true" is 50%; Every question you can come up with, you can come up with a negative version. e.g. "Is your name gwright" vs "Is your name not gwright".
So given any question where you know absolutely nothing at all about it, the probability the answer is "Yes" must be 50%!
The correct answer is the correct answer 100% of the time. And the wrong answer is the wrong answer 100% of the time. If I gave you a question where the correct answer is "no" and you knew _absolutely nothing_ about it, your answer "Yes" would be correct 0% of the time.
That is true, the probability of "Yes" is 0, but only according to you. Relative to me, however, the probability is still 50% chance.
It's just like if there was a stock the market know nothing about, but you know it just scored a magnificent deal a couple of hours ago, the market will see it as "meh, 50 50" (no price change), while you see "100% going to go up, must buy."
So given any question where you know absolutely nothing at all about it, the probability the answer is "Yes" must be 50%!