Mature people are more likely to have heard at least a little bit about Bitcoin to know it's probably worth more than $100. And if they didn't know, they'd probably make some level-headed response (e.g. "I'm not sure what Bitcoin is so I'll take $100"), which wouldn't be as entertaining as two ignorant teenage girls.
And as posted above, it might have taken a while for that guy to find anyone choosing $100 over 1bitcoin.
Its not hard to assume that there are a lot of teenagers who dont know about bitcoin, but at least it should have sparked their interest, if they are offered something to choose from with a hundred dollars, then it can be priced equally, or even cost more.
By the way, this one may also be true that he had to spend some time finding suitable, teenagers who don't know about bitcoin in order to create a headline that would attract attention.