What was this girl trying to tell me? Was she mocking me, or flirting with me, or what?→[More:]

You see the guy in the white shirt all the way over to the right in this photo? I was that using same machine around 8pm on Friday night when this girl comes right up to the window and starts running in place along with me...for like 5 minutes. When I sped up, she'd speed up. When I'd take a bit of a break by crouching and resting on handlebars, she would crouch too and hold her arms up. All the while, she's looking directly at me but not meeting my eyes or changing the neutral expression on her face. What the heck? I didn't really know what to do, so I just kept doing my thing.

To provide a bit of context, "my thing" is pretty intense intervals on the elliptical. I tend to crank up the punk rawk on my mp3 player and zone out, while cranking out my calories as fast as possible, trying not to care what I look like. I use several different body positions to work my legs, arms and core in a variety of ways, mostly in time with my music so it might appear kinda dancey. I usually use the upstairs machines which are not nearly as public as these downstairs machines by the window that get quite a bit passerby foot traffic. The gym is right in the middle of Rockville Town Square, a new development with restaurants and shops and a library. It's a pretty popular hangout spot for local teens and, again, this was Friday night.

So, yeah, it wasn't that unusual when I first started my workout and caught a woman my age turning her head towards me as she went by. Or, a few minutes later, when one of dudes in a group of passing teens obnoxiously gave me a thumbs-up as I looked up after one of my interval-sprints/rock-n-roll-reveries. But then this girl shows up (high school age but I couldn't say whether she was closer to a freshman or a senior, normal-looking, not drunk or anything), gets right in my face and joins in. She was probably less than three feet in front of me, though of course there's a big piece of plate glass between us. Like I said, she never looked me in the eyes, or smiled or laughed at me. I kept doing whatever I would normally do, but I did try look directly at her face occasionally and made a big grin myself after about 2-3 minutes, but no reaction from her. I never turned around to see if anyone in the gym was watching all this, though other people passing by certainly noticed and thought it amusing.

After about five minutes of her copying me, I look up from another interval and find two other girls have joined her and a group of male & female kids were coming up behind them. The new girls were much animated, laughing and just kinda playing along. Their dudes were standing there beside/behind them trying to look cool or whatever. The five minute girl left pretty quickly after these kids show up, looking kinda of sheepish/embarrassed. The new kids didn't keep it up very long, about a minute, and then they stepped back away from the window and just hung out for a few minutes. I didn't notice them looking into the gym while they were hanging out.

When I got home, my wife asked how my workout was and I said "pretty weird" and told her the story. Her reaction was "that's annoying" but not much more. I know kids just do silly stuff sometimes, but I'm really at a loss at how to interpret this. Five minutes* seems like an awfully long time to mock somebody minding their own business (especially given her reaction when the other kids showed up (though, yay, finally some emotion from her!)), but if she was flirting she would have smiled at me or something, eh? I kinda want some feedback from you guys about what possibly could have been going through her mind, because if she was mocking me to that extent I guess I shouldn't use those machines anymore.

This is an estimate of time...it seemed like forever...but I think it's a pretty accurate one based on knowing how long I do certain portions of the elliptical program.