Sounds like she's LYING to you. This is the typical "no interest / just friends" drivel they give to everyone (especially their SO) to make everything seem innocent and harmless as they're meeting "new" men. It's not. Read between the lines. Don't believe anything she tells you. Your gut tells you something is amiss, because it IS. She's not telling the whole truth, and leaving cracks open for a reason.
Why would her "girlfriend" need to have YOUR girlfriend meet this "new" guy? That's likely BS right there, already. Don't believe he flirted with her and she said no, either. They all claim this as they're cheating. Then she wants to go to him - and not the other way around? They're going to hang around in HIS town (where you aren't going to be around) to hang around a little, AFTER he flirted with her?
Sounds like you're being played, or about to be. All the signs are pretty much there, and she's giving you a nice made-up story for it. All I hear is a bunch of BS that makes no sense - because she's LYING. This is a fling in the making.
Here's what likely happened: he met her nearby (or vice versa), he started flirting, they exchanged numbers, texting back and fourth, about to meet and go **** in his town. OR, she's courting him, and seeing if he's a better LTR candidate than you. Either way, its not just a random coincidence.