Personal opinions here: What you have isn't necessarily out of line, in terms of the prose. I've had similar scenes happen to me out of the blue. Not necessarily likely, but they can and do happen.
That said, you're a programmer, and I don't expect miracles in terms of writing. Especially when you're talking about concept pieces early in development. The comments above make a couple of assumptions-- For example, was this the first day of the convention? If not, these two girls could have been watching him for quite some time, and made a conscious decision to act. Or Appreciation could have been following him around to see if he was a jerk, and gotten too close. There's not enough information here to connect all the dots.
Even if it's not the first day, how long is the Convention overall? Most general conventions are 1-3 days, but others have been as long as a week, and in many conventions, a large percentage of people will be locals. The only time you get piles of imports is for specialty conventions with considerable fame attached: E3, PAX, SIGGRAPH, and to a lesser degree AnimeCon in San Diego.
Thus, it's entirely possible (if not likely), that these two girls are from the other side of town, or a nearby town, and may know of him already. There's a lot more here than meets the eye, and if they're close enough to see him next week, they're close enough to have seen him, particularly if he has any sort of local celebrity.
What this scene needs is a little more background, and that's beyond the scope of the document currently being pulled apart. Taken in and of itself, all on it's own, then the ladies upthread have something of a point. But as part of a larger cloth, this scene can stand as-is, or with minor modifications.
Oh, and Crash Into Hello is a trope the way it is, because at Conventions it's pretty much ubiquitous. If you make it through a Con without crashing into someone right before meeting them, you're doing something wrong. Not a new idea, no, but still entirely valid.
I'm going to get off my soap-box now, and let you get back to your day.
Academy Daze- Demo pending
Knights of Chaos: Ghost- Coding underway
Troubleshooter Tales: Childhood's End (story) http://www.knightschaos.com