Does she know its a joke though? I don't see this as an 'I'm obviously joking' text. I see this as a sneaky text. And going off her response, I don't think she got it as a joke either.

Would it give her a laugh? I really don't think it would. I think she'd be left wondering what nutter she's just given her number too who has to send fake texts.

When I was a kid, 15 years old, I'd routinely text some girl something that 'wasn't meant for you'. I don't really see how this is any different.

It being risky has nothing to do with whether she'll text back or not. If thats the case, then every text you send to any girl you've ever met is risky.

The 'Who was that guy?' text is obviously a joke. And the more cocky you can make it, the better. Its designed to immediately break through the 'awkward first text' thing, and to keep her thinking about you after you've gone.