I think it's just coincidence. It's possible that if people are asked to think of a favourite number, it would be likelier for it to crop up if you are performing for a sci-fi fan.
I have some hypotheses on what people tend to pick when asked to think of a random number, and discouraged from picking a favourite number: numbers with few factors, or that have a 3 or a 7 in them. I don't have any evidence to back that up, but that's the feeling I get. As hinted at in the next paragraph, the probabilities of one of these criteria being fulfilled by a true random number generator is quite high (higher than you'd expect) but I still think that the chances of them being picked are even higher with people.
This would lead to some interesting cold reading possibilities if you ask someone to think of a number but you don't know what it is (and they're not trying to catch you out): regarding numbers between 1 and 100, 25 of them are prime, so that would be a good first guess. Failing that, you could fall back to "a few prime factors": an additional 35 numbers are the product of only two prime numbers, for example, so that's a 60% chance of success when I imagine people thinking it's a lot lower than that.
There are 20 numbers that end in a 3 or a 7, and 38 numbers that contain one of these.
I also think people try to avoid repeating digits.
Interestingly, my favourite "random" two-digit number is 43, which is not only prime but has a 3 in it. It is also, by pure coincidence, the number Randall Munroe used in his xkcd comic about human random numbers. And it's close to 42.You can do a lot better than 1% if you start keeping track of the patterns in what numbers people pick.